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This paper presents a method of operating a zeroemission power system in marine vessels. The main goal of the proposed method is to reduce losses of drivetrain devices. The power sources considered in this work are proton exchange membrane fuel cell and lithium-ion battery while the main power consumers are induction motors. Both sources and consumers are connected to a common DC bus through power conversion devices. In the proposed method, the DC bus voltage level is controlled according to the loading of the fuel cells. By controlling the DC bus voltage, it allows operation of fuel cell DC/DC converter in Freewheeling mode which significantly reduces the converter losses. In addition, this approach is also expected to reduce the motor and battery drive losses. Feasibility of the proposed operation method and loss calculations are presented on a realtime hardware-in-loop simulator consisting of real control units and virtual power device models.

Abstract-Operability and dependability metrics can be a valuable tool in early ship design by providing a quantitative analysis of the robustness of the ship's integrated engineering plant (IEP). However, the use of these metrics involves large numbers of time domain simulations of the IEP. The simulation of such a complex system, which includes electrical and thermal subsystems, can be problematic in terms of computational efficiency. In this paper, a simplified modeling approach based on the fundamental power limitations is set forth. The power flow problem is posed as a linear programming problem which is solved using a simplex method.

Abstract-Medium voltage dc distribution systems are currently of interest for future naval warships. In order to provide hardware validation for research associated with the development of these systems, a low power Medium Voltage DC Testbed (MVDCT) is being constructed. This paper documents the system being constructed and provides some initial test results.

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We present a new field-extrema hysteresis loss model (FHM) for high-frequency ferrimagnetic materials, along with a parameter identification procedure. The model does not involve solving an ordinary differential equation (ODE) and is asymmetric in that it works well under dc bias conditions. In the proposed model, the loss calculations are based on the extrema values of the fields. The model includes the effects of magnetic saturation as well as frequency effects. The model is comparable in accuracy to the ODE-based Jiles-Atherton model, but retains the convenience and computational efficiency of an empirical model. We demonstrate a procedure to characterize the model parameters using the Jiles-Atherton model. We compare magnetic hysteresis loss calculated by our new model with a full time-domain solution, as well as an empirical model, for a sample high-frequency ferrite. We demonstrate the use of the model, and validate the model, by calculating magnetic loss in an EI core inductor operating as the filter inductor in a buck converter. The model and identification procedure are being endorsed as a useful framework for computing magnetic loss in the context of automated magnetic device design.

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This paper proposes a novel approach for operating hybrid fuel cell and battery power systems in marine vessels. The target of the approach is to reduce energy losses in drivetrain devices. In the proposed approach, the DC bus voltage of the hybrid power system is adjusted according to fuel cell operating points, which enables operation in Freewheel mode, and thus significantly reducing power conversion losses. Feasibility of the proposed approach is verified using a real-time hardware-in-loop simulation setup consisting of pre-validated virtual models and real industrial power converter controllers. The results presented in the work illustrate that the Variable DC Approach enables significant improvements in drivetrain efficiencies, and thus providing significant savings for vessel operators. Additionally, Variable DC Approach is shown to eliminate high frequency current ripple at the fuel cell terminals, which can further improve the efficiency and the lifetime of the fuel cells.