Featured research (34)
In this paper, an operation-based reliability assessment framework is proposed for Shore-to-Ship Charging (S2SC) systems including On-Shore Batteries (OSB). The OSB is considered to support the grid under fast charging loads. By the proposed approach, the impact of operational planning on reliability is identified. The main operational parameters considered in the reliability analysis include the charging load power and the charging- and discharging scheduling of the OSB. A hierarchical reliability framework is established where the failure rates of the components are estimated based on the FIDES methodology for physics-of-failure-based reliability prediction. Then, a dynamic failure threshold is introduced to translate the component failure consequences to the system performance into three states – failed, normal, and de-rated operation. Hence, the failure threshold is obtained for a specific set of operational and system design parameters. Additionally, to benchmark the characteristics of the SoC profiles of the OSB, an operation-based battery lifetime analysis is conducted. The evaluation of system-level reliability and on-shore battery lifetime is carried out for a 4MW dc S2SC system with a specified range of operation parameters. The results show that batteries and the IGBTs in the power electronics converters are the most reliability-critical elements. Moreover, it is apparent from the results that adjustments to the OSB power profile planning can potentially improve the reliability of the system for specific system sizing. It is also found that the OSB lifetime can be extended up to 2.5 times by increasing the capacity by 50 % and keeping the SoC close to around 50%.
This article proposes a framework for stability analysis of hydrogen fuel cell-based hybrid power systems (HPS) for zero-emission propulsion. An analytical model is developed and a comprehensive modal analysis is performed to address the HPS dynamic interactions. Sensitivity analysis assesses the impact of operating conditions, control parameters of the governor and converter controllers, and different control strategies. The case studies focus on how the parameters of the HPS state variables are coupled with the HPS modes through participation factors (PFs), thereby emphasizing which system state participates in determining the system’s dynamics. The modal analysis characterizes the influence of control parameters on poorly damped modes, and enables expanding the stable operating region of the HPS by appropriate control parameter selection. The results indicate a notable impact of the voltage control loop parameters on the system stability, a strong coupling between the subsystems’ current state variables and dc bus voltage dynamics, and a strong coupling between the governor dynamics and the FC current state. Additionally, the study demonstrates a PF of 0.9 between the dc bus voltage and the HPS’s critical modes within 15% deviation by changes in the voltage controller’s proportional gain. Finally, analytical analysis and time-domain simulations are validated with a real-time hardware-in-the-loop (HIL) test setup.
Ship power and propulsion systems are being electrified for several reasons out of which emission reduction, energy efficiency improvement, and ultimately reduction in operating expense (OPEX) are the main drives. Electrification can be described as the transformation from the conventional transmission system to an all‐electric transmission system linking the energy source and generation units to the power consumers. Here, a marine energy system will be established based on a so‐called hybrid power system composed of three main sub‐systems such as power generation, load (mainly propulsion), and energy storage systems (ESSs). In an electrified marine system, all three main elements can be converted to electric by rotatory electric machines and solid‐state devices such as power converters. The main stem of the system is a power distribution system so‐called switchboard which can be either AC or DC or a combination of them depending on the vessel's mission and function. The connectivity, interoperability, and seamless functioning of such hybrid systems are provided with a hierarchical control system, which includes a power and energy management system (PEMS) as well as low‐level controllers, propulsion control systems, and dynamic positioning (DP). Three key enablers can be seen at the forefront of the green shift, such as electrification of the powertrains and shifting to all‐electric drive; hybridization of the onboard power systems with ESS; and alternative fuels and corresponding energy conversion technologies such as fuel cells (FCs) and gas engines. The electrification has been realized based on the development of power electronics and onboard power systems among them shipboard DC grids. The recent trend of shifting from the conventional AC power system to onboard DC systems is driven by various factors including energy efficiency, control flexibility, design flexibility, and fuel flexibility facilitating the integration of emerging power sources based on alternative fuels, such as H 2 and other low‐emission gaseous fuels. Here, electrification shall be distinguished from battery installation and usage. Electrification in the general form is referring to an all‐electric powertrain with or without batteries. On the other hand, the hybridization of onboard power systems is increasingly implemented due to the advancements in lithium‐ion battery technologies. The batteries are contributing to different aspects of the system operation such as efficiency improvement and consequently fuel and emission saving, dynamic stability improvement, and zero‐emission propulsion. In addition to the efficiency improvement benefits, power smoothing of conventional engines is also a significant aspect as it reduces operational costs. Furthermore, the low or zero‐emission FC power systems are shifting the paradigm in shipboard power systems. This chapter discusses watercraft systems from the perspective of power and propulsion system architectures and topologies. Furthermore, the strategies of control and load sharing are discussed mainly relevant to DC hybrid power systems. Besides, a few case studies are given to elaborate on the efficiency aspect of the onboard DC power system.