Abstract-Marine high-power on-board electrical systems are predominantly utilizing three-phase medium voltage alternating current (MVAC) distribution. Depending on the size and purpose of the ship, on-board electrical systems provide supply to loads in excess of 60MW. Increasingly, medium voltage direct current (MVDC) distribution systems are being considered as an alternative. An increase in the fuel efficiency of the prime movers, the removal of bulky low frequency transformer and the easier integration of different storage technologies are especially attractive. This paper discusses the opportunities but also the technical difficulties associated with the transition from an MVAC to an MVDC system, using an existing LNG tanker MVAC on-board distribution system, as example.

Abstract-Medium-voltage direct-current (MVDC) distribution is a possible replacement due to the advancements in power electronic technologies, for existing medium-voltage ac distribution on ships. The new systems based on MVDC are expected to increase fuel efficiency, remove bulky lowfrequency transformers used for voltage coordination, and integrate storage technologies. These expected benefits of MVDC come with challenges such as stability and reliability of the new distribution system. In this paper, the effect of three different source-side converters, based on commercially available technology, on the MVDC distribution grid and their interactions with the constant power loads (propulsion drives) are investigated. Additionally, the effect of variations in the filtering effort and the distribution lengths on the system stability is analyzed using the impedance-based stability assessment.Index Terms-Impedance-based stability, mediumvoltage direct-current (MVDC) systems.

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Advances in the power electronics technologies, over the years, have opened up possibilities to consider mediumvoltage dc (MVDC) distribution network as a possible evolution of the existing medium-voltage ac (MVAC) distribution networks on large ships. 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 standardised equipment, system-level stability, etc. This work studies the feasibility and stability of MVDC distribution networks when a distributed layout is considered. Due to the nature of the network, a multi 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 i) realistic identification of feasibility limits, ii) definition of design rules for capacitance sizing and best placement and iii) evaluation of distances for dc distribution cables and their corresponding inductances.

Abstract-Generalized State Space Average Modeling (GSSAM), of switching converters, offers an opportunity to improve fidelity of a model by inclusion of different harmonic components. Yet, the inclusion of each frequency component contributes to an increase in the number of the state variables and matrices describing the system. In this paper, automated arbitrary order generation of the GSSAM models for switched DC-DC converters is described, which uses State Space Average Model (SSAM) as starting data set. The buck, boost and buck-boost converters are used as examples and comparison between SSAM, GSSAM of different order and PLECS switched model has been carried out to demonstrate improvements in fidelity of models. Finally, closed loop control with arbitrary order GSSAM is shown using Buck converter as an example.

Abstract-With the improvement in the power electronic technologies, medium voltage dc (MVDC) electrical distribution systems are being considered for on-shore and off-shore applications. These future MVDC electrical distribution systems are expected to provide the possibility of easy interfacing of the renewable energy sources, improving the dynamics of the system and also help in reducing the carbon footprint of energy sources. Modular multilevel converters (MMCs) are used in high voltage dc (HVDC) applications and are being considered for MVDC applications as well. In this paper, we present an MVDC electrical distribution system where the source converter is an MMC and the loads exhibit bandwidth limited constant power load (CPL) behaviour. An analysis is carried out on the dynamic interactions between the MMC source converter and CPLs, considering varying distribution cable lengths between the source and the load, the filtering effort at the load end and different loading conditions.

Abstract-Impedance stability methods are suitable for assessing the dynamics of power converters controllers, but also for ac/dc microgrids system level studies. This work proposes the combination of impedance modeling and conformal mapping for the identification of the dominant eigenvalues. The methodology is derived by linearization of the Cauchy-Riemann equations, which define the conformal mapping property of the Nyquist trajectories. The proposed technique is of high practical value, since it can be performed from frequency-domain data obtained by small-signal perturbation (i.e., explicit transfer functions are not needed). A detailed study case, focused on a medium-voltage dc microgrid, is provided in order to verify the theoretical approach. The new features and limitations of the proposed technique are summarized in the conclusions.Index Terms-ac-dc power conversion, dc power transmission, power system modeling, power system stability, stability criteria.

Abstract-This paper presents comparative evaluation and explores the different technologies suitable for the implementation of the Medium Voltage Direct Current (MVDC) electrical supplies for the marine on-board electrical distribution network. To realize the MVDC supply in the range from 5 kV to 25 kV, various technological choices are available during the design process and have a direct influence on the overall system performances. In this work we discuss different prime movers, choice of electrical generators and type of rectifiers. Different configurations are characterized with different metrics, in terms of commercial availability, quality of supply, efficiency, dynamic performance and volume. Multi-phase multi-pulse supply configurations are identified to provide high quality dc supply and recommended for marine MVDC distribution.