Due to international commitments to reduce emissions in the shipping sector, new fuels and drivetrains are being explored. However, the potential role of batteries is often overlooked in strategic studies. We fill this gap through a broad literature study of grey and academic literature, complemented with three deep dives into Systems Engineering, Sustainable Business Models, and Transition approaches. Battery electric systems are currently the most frequently applied among alternative fuel-drivetrains, although they account for a low percentage of energy use. They are the preferred technology for zero-emission vessels. However, they mostly find application in small to medium hybrid vessels and support functions. Key drivers are regulation and policies, the increase in energy density, and the decrease in costs. Sectoral barriers include infrastructure, the capital intensity of vessels, cost-driven performance, weak governance, and international operations. Challenges for battery applications include integration in a ship's energy system, battery safety, charging, decision support on feasible applications, and establishing viable renewables-based port energy communities that integrate services to and from battery systems on berthing ships. Due to their diversity, versatility, and current application, batteries are likely to become more broadly applied on small to medium-sized vessels, and as enabling technology in hybrid applications and support functions. They thereby have the potential to influence the transition in the sector. Considering the diversity in batteries, shipping segments, and contexts, this will result in many small steps forward. Fast development requires strong policy support. Inherent uncertainty regarding fuels and drivetrains is best countered by robust decision-making in the sector, and can include battery usage.

In the scope of the energy transition, the maritime industry, still heavily relying on fossil fuels, is facing expectations to reduce its carbon output. Electrified shipboard power systems (SPSs) equipped with hydrogen fuel cells (FCs) and energy storage systems (ESSs) are a promising solution for the shift to zero-emission shipping. A remaining challenge is the efficient coordination of multiple parallel power generation and storage modules. This article proposes a modular approach to the power system control to offer a plug-and-play capability for multiple FCs and ESSs, facilitating a topology reconfiguration. Virtual impedance-based droop is implemented to achieve power sharing and load frequency decoupling in a decentralised architecture. An additional low-bandwidth communication is leveraged to enable parameter adaptation after a topology reconfiguration. The methodology is tested numerically with a short-sea cargo vessel serving as a case study. The local controllers are tuned to achieve load frequency decoupling between FCs and batteries matching the specified time constant. For a maneuvering power profile, the average FC power gradient could be decreased by 36%, limiting their degradation caused by dynamic operation, while increasing the depth-of-discharge of the batteries. The simulations further show that an adaptation of control parameters after a component fault can be used to maintain the system’s voltage dynamics. The voltage drop caused by a load step in a reconfigured system that disconnected one of two ESS could be reduced by 37.5% by control parameter adaptation.

Wind energy has witnessed a staggering development race, resulting in higher torque density demands for the drivetrain in general and the gearbox in particular. Accurate knowledge of the input torque and suitable models are essential to ensure reliability, but neither of them is currently available in commercial wind turbines. The present study explores how a subspace identification algorithm can be applied to fiber-optic strain sensors on a four-stage gearbox to obtain operational deflection shapes. An innovative measurement setup with 129 fiber-optic strain sensors has been installed on the outer surface of the ring gears to research the deformations caused by planet gear passage events. Operational deflection shapes have been identified by applying the multivariable output-error state space (MOESP) subspace identification method to strain signals measured on a serial production end-of-line test bench. These operational deflection shapes, driven by periodic excitations, account for almost all the energy in the measured strain signals. Their contribution is controlled by the torque applied to the gearbox. From this contribution, a torque estimate for dynamic operating conditions has been derived. Accurate knowledge of the input torque throughout the entire service life allows for future improvements in assessing the remaining useful life of wind turbine gearboxes.

This paper presents a desaturation-based technique for short-circuit protection in quasi-two-level converters. The proposed design enables a cost-effective implementation of this protection scheme in a flying capacitor multilevel converter operating as a quasi-two-level converter, requiring only two detection circuits for n series-connected switches. Detailed design guidelines for the protection circuit are provided, along with simulations that illustrate its operational boundaries and experimental verification of the proposed scheme.

The development of DC protection systems is an enabler of widespread adoption of DC microgrids. This paper introduces a three-level gate driver that provides the latching current limiter functionality in a solid-state circuit breaker with unidirectional protection. The proposed gate driver combines the output port description of a well-known, enabled gate driver with a soft turn-off network. The corresponding circuit can be adapted to well-established SSCBs, requiring few modifications which could allow for quick development. The concept, simulation, implementation and experimental validation of the gate driver are in the scope of the paper. The gate driver is implemented and tested in a solid-state circuit breaker prototype, showing the potential to develop further DC protection devices.

The electrification of ship power systems plays a center role in the mobility transition towards sustainable transport solutions. It allows the integration of various power sources, energy storage systems, and intermittent generation. The integration of an increasing number of components with distinct characteristics shapes the notion of a shipboard microgrid which benefits from a modular approach in its design to reduce costs and uncertainties. DC distribution facilitates the modular design by simplifying the control, and, combined with power electronics interfaces, increases the controllability of power flows in the system. To handle the increasing system complexity, this work proposes a distributed and predictive control approach, addressing the modular topology of future shipboard power systems and leveraging load power forecasting. Investigations show that a distributed, predictive energy management reaches a similar performance as a centralized implementation. For a modular shipboard power system, the proposed method decreases both fuel and degradation costs with increasing performance gains for longer prediction horizons.

Accurate knowledge of the mechanical loads of wind turbine gearboxes has become essential in modern, highly loaded gearbox designs, as maintaining or even improving gearbox reliability with increasing torque density demands is proving to be challenging. Unfortunately, the traditional method of measuring dynamic mechanical torque using strain gauges placed on the outer surface of a rotating shaft and transmitting the resulting signal is unsuitable for serial deployment due to technical and economic constraints. An alternative method based on fiber-optic strain sensors placed on the stationary outer surface of the gearbox ring gear has been proposed. Like shaft torsion, the radial deformation of the ring gear is proportionate to the rotor torque. Placing the sensors on a stationary component is a cost-effective alternative for serial implementation because the need for complex and expensive data transfer via wireless transmission or a slip ring is eliminated. In this paper, we present the results of an extensive field experiment conducted to evaluate the torque measurement accuracy of this novel sensing solution installed on the gearbox of a Gamesa G97 2-MW wind turbine at the National Renewable Energy Laboratory’s Flatirons Campus. Torque measurements derived from fiber-optic strain sensors placed on the ring gear of the planetary stage are compared to conventional torque measurements from strain gauges placed on the main shaft. Two different torque estimation data processing methods were evaluated, with the method based on operational deflection shapes providing the most accurate results with an average normalized root mean square error below 0.7% for a load revolution distribution analysis. The effect of operating conditions on the torque estimate was also investigated, and the third planet-passing operational deflection shape was found to be the least sensitive to nontorque load-related effects. The fiber-optic strain sensors’ successful operation during the complete test campaign has demonstrated a robust and accurate solution for fleet-wide enhanced gearbox remaining useful life estimation.

A key factor towards zero-emission shipping is the adoption of electric propulsion with hybrid power sources. The heterogeneous power sources of modern electric vessels require optimal energy management systems, as conventional rule-based control in hybrid energy systems may result in suboptimal solutions with limited flexibility. Advanced optimal control strategies offer a promising avenue to address this issue. This paper presents a novel control strategy based on the Equivalent Consumption Minimization Strategy for a dual-fuel full-electric vessel operating with diesel engines and hydrogen fuel cells taking into account both fuel cost and NOx emissions. The effectiveness of the developed controllers is evaluated against a benchmark derived from state-of-the-art strategies in a simulation study using real-world data. The results highlight the controller's performance, as well as the operator's choice by selection of weights for the objectives. The proposed control strategy achieves nearly 2 % fuel savings compared to a single-objective rule-based controller. It also exploits the potential for up to 45 % reductions in NOx emissions. When both objectives are combined, the controller still delivers over 0.5 % fuel savings while reducing NOx emissions by nearly 15 %. If a financial cost is assigned to emissions, the total operational cost savings increase to more than 4 %.

Hybrid power systems are increasingly adopted onboard. Lithium-ion batteries now serve as a viable energy storage solution that enhances fuel efficiency and reduces the operating hours of main power units, thereby reducing operational expenses. However, integrating batteries onboard requires decision-making that accounts for diverse scenarios, including battery chemistry, variations in vessel operational profiles, and fluctuating fuel prices. To address these challenges, this study investigates whether battery sizing and scheduling of the power and energy management system require a scenario-based stochastic decision framework. Specifically, it examines how energy storage requirements are influenced by varying load profiles, whether the optimal battery size and power management strategy are affected by fuel price fluctuations, and how robust the overall strategy remains under operational uncertainties. A deterministic equivalent of a two-stage stochastic decision framework is introduced to incorporate these uncertainties, offering insights into the required battery technology, capacity, and correlated behavior of onboard energy management. Multiple scenarios are applied to a trailing suction hopper dredger, analyzing three load profiles with distinct variations in power demand. With reserve power constraints enforced, the optimal battery capacity remains fixed. However, when these constraints are relaxed, the optimal battery size becomes more sensitive to fuel price changes. In addition, the results showcase reduction in diesel engine operating hours—thereby lowering both fuel consumption and maintenance costs, demonstrating that these operational benefits depend not only on the battery's size but also on its available throughput, which allows for deeper cycling.

Sustainability regulations urge the maritime sector to implement green technologies. The integration of polymer electrolyte membrane fuel cell (PEMFC) systems is a promising solution to cut emissions. However, their degradation in maritime environments is rarely addressed, while the environment differs significantly from land-based or automotive contexts and can greatly affect the type and extent of damage. Research in this field is especially relevant as ships often operate in isolated areas and require durable and reliable power propulsion systems. This work collects the insights from existing PEMFC durability research and analyzes degradation mechanisms specifically relevant for the maritime field. We consider air and fuel contamination, maritime load profiles, and vessel motions as potential causes. Insightful schematics summarize the content by linking these causes to damage indicators. Moreover, we identify various areas for further research including degradation from interconnected effects of maritime drive cycles, marine air salinity, hydrogen-carriers and their residues, long term maritime vibrations, and dynamic inclination. The overview of existing literature combines insights from electrochemistry and maritime research while the knowledge gaps help to prioritize future research. Together, these elements promote collaboration in this multidisciplinary field, advancing mitigation strategies and improving cell, stack, and ship design and operation. Such improvements encourage PEMFCs application in ships and support the move towards zero-emission shipping.

The electrification of shipboard power systems carries an increasing variety in power sources, energy storage systems, and power converters. DC distribution is gaining relevance due to efficiency increase, space savings, and high controllability. The dominant primary control method voltage droop control, which offers easily implementable and scalable power sharing and voltage stabilization. However, compared to terrestrial microgrids, shipboard power systems have low line impedances and highly fluctuating loads. Most primary loads are power-controlled, introducing a non-linearity that leads to a weak damping and unstable operation points. To handle this non-linearity, this study proposes an energy-based control approach as an alternative to the voltage-based scheme. The controller is further extended by integral feedback loop to achieve fast voltage restoration. A low-bandwidth communication is leveraged for an adaptive power sharing control that facilitates an efficient allocation of the load among parallel units under varying conditions. The proposed control structure is deployed on an I/O board embedded in a hardware-in-the-loop testbed. It is shown that the energy-based controller operates stably and achieves a reduced voltage deviation from the nominal voltage in various load conditions compared to the conventional voltage-based method.

This paper proposes an integrated gate driver featuring soft turn-off and current limiting for a solid-state circuit breaker in primary shipboard DC systems. The added functionalities allow solid-state circuit breakers to mitigate part of the voltage resonances caused by a hard turn-off, and to reduce unnecessary tripping during overloading events. The proposed design is based on well-known DC protection strategies, which are enhanced by the custom gate driver, simulated in SPICE software. The paper shows that the proposed strategy effectively attenuates the adverse effects of the hard turn-off present in popular off-the-shelf devices, while effectively breaking the fault current. The low propagation delay of the selected components facilitates the rapid break of the current, reaching approximately 69A peak. In addition, the latch current limiter prevents the feeder from overloading, creating a voltage drop of 51% for tens of nanoseconds. The results are promising in motivating future prototyping of the design in an attempt to accelerate the acceptance of shipboard DC systems.

The current state of research in marine energy systems has concentrated on conventional diesel systems, while limited literature is available on the configuration and control of alternative energy sources such as hydrogen hybrid systems, which have attracted increasing interest recently owing to the energy transition. This paper presents a modelling and control study for conceptual retrofitting of a general cargo vessel to a hydrogen-hybrid version. Generic fuel cell, battery, and converter models are used, enabling easy adaptation to various powerplant sizes and ship types. A robustly coordinated Energy Management Strategy (EMS), which can be implemented for different vessel’s power profiles, was developed for power sharing, DC bus voltage control, and battery State of Charge (SoC) regulation. The total installed fuel cell power and battery capacity were heuristically selected from a range of power profiles of the ship. A database of fuel cells with stacks from different manufacturers was created to test different combinations in terms of fuel consumption, cost, and weight, based on the framework of the problem. Uncertainties in terms of fuel prices are presented using normal distribution graphs. The system configurations and control results are presented for one power profile of the vessel and the average fuel costs. It is demonstrated that with the proposed control method, the power losses are less than 1%, the DC bus voltage fluctuations are less than 0.5%, and the battery SoC remains between 35-65% for the entire duration of the analysed power profile. The configuration with eight stacks of 150 kW has the lowest total fuel cost (730 $) with an average difference of 7.1% from the other solutions, and the lowest total weight (10.54 tons) with an average difference of 15.4% from the other configurations. Overall, this study demonstrates the efficient configuration and control of hybrid energy systems using parameterized components.

Switching to Proton Exchange Membrane Fuel Cell (PEMFC) systems can greatly reduce the environmental impact from the maritime industry. However, the limited durability of PEMFCs remains an obstacle for their implementation. Understanding fuel cell degradation is especially relevant for ships, as they typically operate for long periods and in isolated areas. Their energy systems therefore need to be exceptionally robust and reliable. In order to improve the design of maritime PEMFCs, we need to improve our understanding of degradation mechanisms induced by their use on a ship. Models can be a great tool to that end.
Many PEMFC models have been developed and used over three decades. They differ on various levels, from their spatial dimensions – one, two or three dimensional – to which processes are modelled and the detail to which they are described. Our previous review1 shows that numerous processes contribute to degradation in a maritime context. These include more general processes, such as load induced damage, as well more specific ones for ships, such as sea salt contamination via the air inlet.
Currently, there is no modelling framework to quantify PEMFC degradation in a maritime environment specifically. The aim of this work is to propose such a framework, building on knowledge gained from previous modeling studies. It should integrate the additional degradation triggers such as salt contamination. We start out by analyzing existing PEMFC durability models. They are rated based on the coding complexity, computational costs, specificity and the possibility to incorporate both specific
maritime as well as general degradation causes. Thereafter we analyze whether and how the models are validated and verified.
The proposed modeling framework can serve as a blueprint for future maritime PEMFC degradation models. These can facilitate vessel specific case studies, investigations to improve cell and stack design and explorations of altered ship operational profiles. The resulting insights will aid scientists, engineers and ship owners to improve PEMFC lifetime in maritime applications.

A degaussing system can be used to reduce the detectability of the magnetic signature of a ship. Commonly, a degaussing system consists of a set of onboard copper coils that produce a magnetic field to compensate for the magnetic signature. High-temperature superconductive degaussing coils are considered an alternative to copper degaussing coils because of a reduction in energy losses, weight, volume, and costs. The losses of a high-temperature superconductor (HTS) degaussing system can be reduced even further by powering it with a cryocooled converter with parallel mosfets. A low-duty cycle and smaller current leads can be used. These solutions eliminate most of the power source losses. This article investigates such a cryocooled converter. The effect of the low switching frequency on the converter performance is tested. A prototype that can operate at cryogenic temperatures was built. The converter powers an HTS coil. It was found that a load current of 50 A can be achieved with a duty cycle of just 0.025 at an input voltage of 3.5 V while still meeting the requirement of a maximum current ripple of 0.5%. At a switching frequency higher than 100 Hz, the converter's performance deteriorates. Also, oscillations were observed in the circuit. This is a problem due to the low blocking voltage of the mosfets. The parasitic inductances in the circuit have a high impact on the performance because the resistance in the circuit is very low.

The protection of DC systems in mobility applications, such as land transport, aircraft, and shipping, presents significant challenges due to the need for high power density equipment in confined spaces. This paper focuses on DC systems on board ships, for which diverse applications require different power levels, architectures, and protection strategies. Existing protection frameworks and regulations are often inadequate or outdated for the field, leading to certification issues and insufficient fault analysis. This research proposes a use case-based categorization of short circuit currents for primary systems. A reference scenario is created using a simulation model of a 5 MW system in a superyacht to provide a short circuit inventory. The study proposes three contributions. A comprehensive fault inventory, a qualitative categorization, and relevant recommendations for power converter design. The research highlights the importance of fault categorization in understanding the impact of various short circuits on shipboard DC systems. The study emphasizes the importance of the evolution of materials and power converters in developing efficient protection technologies for ships. This work addresses some fundamental gaps in shipboard DC systems, providing a foundation for improved protection strategies and regulations, ultimately contributing to the advancement of protection of shipboard DC systems.

Hydrogen-based shipboard power systems (SPS) are gaining prominence as a zero-emission alternative to conventional diesel-fueled systems for reducing the carbon footprint in the maritime sector. Typical designs incorporate fuel cells (FCs) as the main power supply combined with batteries in a DC distribution network. However, the efficient coordination of power generation and storage systems with different characteristics remains a challenge, particularly in topologies with multiple parallel FCs and batteries. This aspect has received limited attention in existing research. To address this challenge, this paper presents a modular approach to the hierarchical control of power generation and storage systems. Dynamic power sharing is achieved using a decentralized strategy that employs bandwidth separation, accounting for the opposing capabilities of each device. Additionally, an energy management strategy (EMS) based on equivalent consumption minimization is realized in this modular framework using a low-bandwidth communication network. The proposed architecture's modular character allows for a flexible power system reconfiguration and extension. The methodology is showcased through simulations using a short-sea cargo vessel as a case study. The results demonstrate that the bandwidth separation ensures the operation of the different technologies within their specified bandwidths, limiting the potential degradation of the FC systems. The addition of the modular EMS shows a fuel-efficient operation of the FC-battery DC SPS and a decrease in the FCs' power gradients, and thereby their aging effect.

Optimal energy management is still a challenge in full-electric vessels. New degrees of flexibility in the energy management resulting from the load sharing between multiple, heterogenous power sources lead to a suboptimal solution using rule-based control. Therefore, advanced control strategies present a solution to the challenge of finding the optimal control input for a nonlinear multi-objective power and energy problem in sufficient time. As additional benefit, advanced control allows to incorporate multiple objectives in the optimization such as minimization of several emissions, operational costs, and component degradation. Equivalent Consumption Minimization Strategy (ECMS) is a strategy for instantaneous optimization, which is promising for applications in vessels with a high degree of uncertainty in the load profile. It incorporates multiple objectives by assigning equivalent cost factors in the cost function, allowing a flexible expansion of the control problem. In this paper, we present a novel ECMS-based control strategy for a full-electric vessel with the ability to react flexibly to changing mission conditions. First, we define the objectives for the control problem, in this study \ce{CO2} production, hazardous emission production, fuel consumption, energy cost, and the degradation of the battery.
Second, we develop a pareto-front approach for a-posteriori definition of the equivalent cost factors. To showcase energy consumption reduction, we use a benchmark control based on state-of-the-art control strategies. A full-electric case study vessel with high uncertainty in the load profile is chosen to evaluate the proposed controller. Several different load profiles are generated and tested to evaluate the performance of the ECMS controller in dealing with different types of loads. The results will demonstrate the effectiveness of the proposed novel control strategy in reducing energy consumption while minimizing other hazardous emission outputs and preserving the health of the battery.

The mesh load factor, K 3, describes how loads are shared between planet gears and has become one of the key design challenges in modern wind turbine gearboxes. Planet load sharing directly impacts tooth root stresses, a critical driver of torque density and gearbox reliability. Experimental evaluation of K 3 is typically performed from sun gear tooth root strain gauge measurements, which are complex. Furthermore, such measurements can only provide an average value of load sharing. The present study describes an alternative method to evaluate the mesh load factor in wind turbine gearboxes based on fiber-optic strain sensors installed on the outer surface of the fixed ring gear. We present the results of an extensive measurement campaign to evaluate this novel sensing solution installed on the input planetary stage of a 2-MW wind turbine gearbox at the National Renewable Energy Laboratory's Flatirons Campus (Colorado, USA). The number of strain sensors on the ring gear was selected as an integer multiple of the number of planets, which has enabled an instantaneous evaluation of the mesh load factor. The effect of operating conditions on the planet load-sharing behavior of the gearbox has been investigated. The mesh load factor measured for operating conditions close to rated was below 1.05, well below IEC 61400-4 standard requirements.

Fuel cell-battery electric drivetrains are attractive alternatives to reduce the shipping emissions. This research focuses on emission-free cargo vessels and provides insight on the design, lifetime operation and costs of hydrogen-hybrid systems, which require further research for increased utilization. A representative round trip is created by analysing one-year operational data, based on load ramps and power frequency. A low-pass filter controller is employed for power distribution. For the lifetime cost analysis, 14 scenarios with varying capital and operational expenses were considered. The Net Present Value of the retrofitted fuel cell-battery propulsion system can be up to $ 2.2 million lower or up to $ 18.8 million higher than the original diesel mechanical configuration, highly dependent on the costs of green hydrogen and carbon taxes. The main propulsion system weights and volumes of the two versions are comparable, but the hydrogen tank (68 tons, 193 m³) poses significant design and safety challenges.