Ship hybridization has received some interests recently in order to achieve the emission target by 2050. However, designing and optimizing a hybrid propulsion system is a complicated problem. Sizing components and optimizing energy management control are coupled with each other. This paper applies a nested double-layer optimization architecture to optimize the sizing and energy management of a hybrid offshore support vessel. Three different power sources, namely diesel engines, batteries and fuel cells, are considered which increases the complexity of the optimization problem. The optimal sizing of the components and their corresponding energy management strategies are illustrated. The effects of the operational profiles and the emission reduction targets on the hybridization design are studied for this particular type of vessel. The results prove that a small emission reduction target of about 10% can be achieved by improving the diesel engine efficiency using the batteries only while the achievement of a larger emission reduction target mainly depends on the amount of the hydrogen and/or on-shore charging electricity consumed. Some design guidelines for hybridization are derived for this particular ship which could be also valid for other vessels with similar operational profiles.

Modularity is promising from a view to increasing turbine availability through fault tolerant operation as well as reduced downtimes, especially for offshore wind turbines. This paper focuses on a quantitative analysis of large scale (or extreme) modularity in power electronic converters of wind turbine generator systems. It uses mathematical models to investigate the effect of the choice of module number on the availability of a converter. It further analyses the availability in conditions where increased levels of modularity lead to a reduction of failure rates in the system. The paper extends this analysis by quantifying the benefits for a 10MW case study turbine. Finally, it concludes that extreme modularity holds merit only when it is accompanied by a reduction in failure rates.

This paper proposes a simplified approach to model the thermal behavior of the insulated gate bipolar transistors (IGBTs) in a subsea power electronic converter. The models are based on empirical relations for natural convection in water, and IGBT datasheet values. The proposed model can be used in the design of subsea converters and in the reliability analysis of their IGBTs. Experimental results are provided to validate the proposed thermal model. Suggestions are made to minimize the net thermal resistance by introducing a high conductivity thermal material as a mounting plate between the IGBT and the cabinet walls. Impact of the mounting plate dimensions, and material properties on the junction temperature of the IGBTs is studied. A case study analysis is made on a 100 kVA converter. Results indicate that the thermal spreading resistances in the mounting plate and the cabinet walls contribute significantly to the overall thermal resistance. Spreading resistances can be mitigated by appropriate design measures. Furthermore, it was observed that the passive cooling in water is not as effective as the forced water cooling. However, the low cost, simple design and higher reliability of passive cooling systems might make them a favorable choice for subsea systems.

The power electronic converter, especially the power semiconductor, is a major contributor to the failure rates of the wind turbine drivetrain. As the temperature is a major driving factor behind the failure mechanisms of these power semiconductors the choice of topology and switching strategy can have a significant effect on the reliability of the converter. This paper presents a detailed comparison of several three level converter topologies and switching strategies on the basis of loss distribution, thermal, and lifetime performance. This investigation is done through simulations on a 10MW direct drive permanent magnet drivetrain. The study shows that over-rating in the form of using overrated topologies, or the use of overrated components can result in large gains in lifetime expectancy and quantifies these gains. It concludes that the improvements offered by overrated topologies and overrated components are comparable and that use of the overrated topologies do not offer a significant advantage over the use of topologies with overrated components.

The brushless Doubly-Fed Induction Machine, without brushes and slip-rings, is regarded as an attractive alternative to the conventional Doubly-Fed Induction Machine in terms of reliability. This paper presents a sensorless field oriented control strategy for the Brushless-DFIM, which further increases its attractiveness as a drive system.With the use of a straightforward and alternative time-dynamic Brushless-DFIM model, a complete Brushless-DFIM based drive is modelled and used for the development of the sensorless control strategy. The developed sensorless control strategy is implemented in an experimental set-up. Simulation and measurement results demonstrate that the developed sensorless control strategy can control the Brushless-DFIM in a stable and responsive manner over its full operating speed range. In this way, a fully functional sensorless control strategy for the Brushless-DFIM is demonstrated for the first time in literature.