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In a fault situation on a microgrid with multiple sources, a ring distribution architecture permits healthy parts of the power distribution network to remain operational while isolating a fault. However, fault localization in a multi-ring power distribution system can be considerably more complex than for a radially distributed network. This paper presents a nonintrusive approach for making microgrid protection systems aware of load operating condition in order to improve fault detection, e.g., for detecting destructive high-impedance and arcing faults.

As part of the U.S. Navy’s continued commitment to protecting U.S. interests at home and abroad, the Navy is investing in the development of new technologies that broaden U.S. warship capabilities and maintain U.S. naval superiority. NAVSEA is developing power systems technologies for the Navy to realize an all-electric warship. New nonlinear power system controls approaches are being developed to improve system performance in light of new electrically powered weaponry that behave as pulsed-loads. Advancements include the identification of pulsed-load profiles that identify Energy Storage System (ESS) requirements. A dynamic optimization engine has been developed and serves as the feedforward receding horizon control portion of the Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) feedback controls for ESS networked microgrid system. A Coalition Warfare Program (CWP) test scenario was selected. The CWP is defined with a Reduced Order Model (ROM) that includes; generation, ESS, and mission pulsed-loads. Several numerical simulation studies were conducted. The CWP scenario is bounded by a baseline mission load local ESS contrasted with no ESS full nonlinear metastable boundaries. The main goal is to minimize ESS size and weight while maintaining power system performance. This paper focuses on the control and optimization of ESS as an integral part of supporting critical mission loads and real-time control algorithm development to improve future energy efficiency for multi-mission activities.

As part of the U.S. Navy’s continued commitment to protecting U.S. interests at home and abroad, the Navy is investing in the development of new technologies that broaden U.S. warship capabilities and maintain U.S. naval superiority. In particular, NAVSEA is supporting the development of power systems technologies that help the Navy realize an all-electric warship. It is recognized that a challenge to fielding an all-electric power system architecture includes minimizing the size of energy storage systems while maintaining the response times necessary to support potential pulsed loads. This work explores the trade-off between energy storage requirements (i.e. size and weight) and performance (i.e. bandwidth and storage) in the context of a power system architecture that meets the needs of the US Navy. To compare energy storage technologies and appropriately size them, it is necessary to specify size and weight requirements and thus consider the energy density of the technology in Wh/kg and specific power density in W/kg. The modelled time domain behaviour for different load types and control delays were used to determine technology and sizing requirements by comparing the total energy and maximum power used in the simulation to a Ragone plot. Simulation results based on operational vignettes were used to identify a range of specific power and energy densities that will meet system requirements. Potential energy storage sizing can be determined by approximating where a selected technology intersects with the energy and power requirements of the system. Another major component necessary to determine energy storage technology is the frequency domain behaviour of the system. In this work, the energy storage control bandwidth is evaluated in simulation for different loading scenarios, and a trade-off between size/weight and response bandwidth is illustrated.

Many candidate power system architectures are being evaluated for the Navy’s next generation all-electric warship. One proposed power system concept involves the use of dual-wound generators to power both the Port and Starboard side buses using different 3-phase sets from the same machine (Doerry, 2015). This offers the benefit of improved efficiency through reduced engine light-loading and improved dispatch flexibility, but the approach couples the two busses through a common generator, making one bus vulnerable to faults and other dynamic events on the other bus. Thus, understanding the dynamics of cross-bus coupling is imperative to the successful implementation of a dual-wound generator system. In (Rashkin, 2017), a kilowatt-scale system was analysed that considered the use of a dual-wound permanent magnet machine, two passive rectifiers, and two DC buses with resistive loads. For this system, dc voltage variation on one bus was evaluated in the time domain as a function of load changes on the other bus. Therein, substantive cross-bus coupling was demonstrated in simulation and hardware experiments. The voltage disturbances were attributed to electromechanical (i.e. speed disturbances) as well as electromagnetic coupling mechanisms. In this work, a 25 MVA dual-wound generator was considered, and active rectifier models were implemented in Matlab both using average value modelling and switching (space vector modulation) simulation models. The frequency dynamics of the system between the load on one side and the dc voltage on the other side was studied. The coupling is depicted in the frequency domain as a transfer function with amplitude and phase and is shown to have distinct characteristics (i.e. frequency regimes) associated with physical coupling mechanisms such as electromechanical and electromagnetic coupling as well as response characteristics associated with control action by the active rectifiers. In addition, based on requirements outlined in draft Military Standard 1399-MVDC, an approach to derive specifications will be discussed and presented. This method will aid in quantifying the allowable coupling of energy from one bus to another in various frequency regimes as a function of other power system parameters. Finally, design and control strategies will be discussed to mitigate cross-bus coupling. The findings of this work will inform the design, control, and operation of future naval warship power systems.

Selection of power and propulsion system architecture is one of the most far-reaching and irreversible decisions made by the designer of a modern ship. However, most texts and design handbooks pay little attention to the implications of this design decision nor is sufficient attention paid to the attributes of the various alternatives available to the ship designer/owner. Integrated power systems, made possible over the past three decades by the advances in modern high-power power electronics, provide many benefits to the ship owner, including reduced operating costs, arrangement flexibility, superior reliability and survivability, and support for advanced weapons on sensors warships. This paper will outline the architecture options available to today’s ship designer and will discuss the design implications and pitfalls inherent in the power system architecture selection, paying particular attention to the unique aspects of integrated power systems.

Aspects of terrestrial microgrids and ship power systems are examined. The work exposes a variety of technical synergies from these two power systems to effectively advance their technologies. Understanding their overlap allows congruent efforts to target both systems; understanding their differences hinders conflict and redundancy in early-stage design. The paper concludes by highlighting how an understanding of both systems can reduce the investment in research resources.

Several technical power system architectures are being evaluated for the Navy's next generation all-electric warship. One concept being considered includes a scheme to power both port and starboard busses from a single generator with dual-windings. This approach offers redundancy and reduces the effects of prime mover light loading, but it inherently couples the two busses through the common generator. In this work, dynamic issues of galvanic and electro-mechanical coupling of power systems through a single dual-wound generator are discussed. Previous works focused on harmonics and galvanic coupling. Herein, focus is placed on average-value modeling of the galvanic coupling and on evaluation for fault response. Conclusions are presented from analysis, simulation, and experimental results.

The first of the Arleigh Burke class destroyers is nearing its mid-life. This class of ships was designed during the late 1970s through the 1980s to meet the threats that were prevalent at that time. Since entering service in 1991, these ships have shown themselves to be extremely versatile and the class now consists of nearly 60 ships in service. Their combat systems have been continually upgraded and adapted to meet the new threats the United States faces today. However, in order to keep these platforms viable throughout the first half of the 21st century, their operating costs must be reduced. Manpower, maintenance, and fuel are three of the top operating cost drivers. Most surface combatants spend very little of their underway time operating at full speed or even close to that. Over 1/3 of their underway time is spent at 12 knots and under. This is less than half of their maximum speed and only a fraction of the maximum power owing to the cubic speed-power relationship. Although the existing mechanical drive system is reasonably efficient, the main gas turbines are extremely inefficient at these very low power levels. A shaft-mounted auxiliary electric propulsion system (EPS) can take advantage of excess capacity in the ship service generators to reduce the main engine operating hours. Enabling bi-directional power flow from this auxiliary electric drive will provide additional generation capacity for ship service loads at a modest additional cost. It also provides a "cross-connect" capability from one shaft to the other. This paper will explore one prospect for reducing the operating cost of the DDG-51 class of ships by installing an auxiliary EPS that would powered by the ship service electrical plant. This additional system would serve to reduce both underway fuel usage as well as maintenance on the gas turbine main engines by reducing the number of operating hours on each engine. We will examine the technology trade-offs in this ongoing study.

There are essentially two kinds of power and propulsion system architectures in use today: Segregated and Integrated. The hybrid architecture combines aspects of both of these into a single ship design. It can also be considered to be partially integrated power system architecture. Dalton [1] describes the trade-offs in selecting power system architectures.

Mercury has always held the distinction of being the terrestrial planet most unlike the others. On 18 March 2011, after three successful flybys of Mercury, the MESSENGER spacecraft entered orbit around Mercury. Essential to the payload of MESSENGER are three instruments designed to measure the geochemistry of the surface – an x-ray spectrometer, a gamma-ray spectrometer, and a neutron spectrometer. Together, the data returned by these three instruments – coupled with insights about planetary structure gained from tracking the spacecraft, spectral data measured in orbit, and a new and complete view of the geology of the surface – have begun to revolutionize the people's understanding of Mercury. In this chapter, the authors first review the pre-MESSENGER views of Mercury, followed by the first results from the MESSENGER mission. The authors then discuss the implications of these first results in constraining the origin of Mercury, followed by looking forward to future work.

Dramatic improvements have occurred since the large AC synchronous - wound field - conventionally cooled motors went to sea on Queen Elizabeth 2, podded propulsion motors not even having been discussed. Electric propulsion motors have become smaller, better and more affordable. Electric propulsion motor drives have followed a similar trend. Subsequent improvements, in both naval and commercial ships, are almost certainly going to be implemented using the systems and technologies which offer the best Life-Cycle Cost benefits; thus ocean-going ships, including naval combatants, will continue to most affordably transport either cargo or a military mission capability.

This paper discusses the electrical and magnetic design and analysis of a permanent magnet (PM) generation module for naval applications. Numerous design topics are addressed and several issues are raised about the potential improvements a PM generation system can offer. A proposed 16 MW PM generation module design is presented along with a design methodology. The final design offers significant reductions in both weight and volume. Specifically, it is estimated that the PM generation module has a 7x reduction in volume and a 10x reduction in weight compared to similarly rated wound rotor systems. These reductions can provide flexibility to naval architects since power, weight, and volume are integral parts of the design and construction processes. However, further study is necessary to verify the PM generation modules thermal, structural, and mechanical performance.

Field studies have demonstrated that the non-intrusive load monitor (NILM) can effectively evaluate the state of many electromechanical systems by analyzing the electrical power that they draw. This paper discusses NILM applications in the marine environment. Machinery power data collected from USCGC SENECA (WMEC-906), a 270-foot U.S. Coast Guard cutter, indicates that the NILM can successfully diagnose the failure of flexible couplings and the presence of leaks in cycling systems. This paper discusses both of these shipboard problems, and it details the methodology used to develop the metrics that diagnose them.

Since the 1980s there has been an explosion in the number and variety of electric propulsion ships being built around the world with everything from cruise liners to amphibious assault ships adopting electric propulsion. This technology revolution has occurred, largely un-noticed outside the marine industry. This paper briefly describes what has transpired in recent decades, why the resurgence is occurring and what the future may hold for electrically propelled ships.

Alstom Drives and Controls, Ltd has developed under US Navy sponsorship a novel 19 MW PWM motor and drive for use in naval ship propulsion applications. The design requirements for this application placed stringent constraints on the size and acoustic signature of the motor and drive. When combined, these requirements create a very difficult electromagnetic compatibility (EMC) problem for the motor drive. This paper describes the drive requirements, EMC features designed into the drive as well as lessons learned from the component and factory testing and from the commissioning of this unique drive.

Cell lines of Medicago sativa have been selected for resistance to the toxin(s) produced by Fusarium oxysporum f. sp. medicaginis. Selected cell lines showed resistance in vitro on media containing F. oxysporum culture filtrate. Plants regenerated from resistant cell cultures showed resistance to the pathogen in two greenhouse studies. In addition, cell lines reinitiated from regenerated plants showed resistance on the media containing culture filtrate. Initial resistant selections from long-term culture showed elevated ploidy levels (octoploid and hexaploid). Subsequent selections of resistant cell lines from a shorter selection cycle yielded resistant plants with the normal tetraploid chromosome number.

Chromosome manipulation and breeding were used to produce a cultivated diploid alfalfa clone (HG2) which possessed the ability to regenerate plants from suspension cultures. Callus colonies and regenerated plantlets were obtained at a planting density as low as 2 · 10 3 cells/ml, but colony development was enhanced by greater density, and 2 · 10 4 cells/ml was near the optimum. Ability to regenerate (96% of colonies) and the proportion of diploid plants (70%) both remained high after one transfer and a total of 21 days in suspension. Regeneration decreased with time in suspension culture to 48% at 56 days, 3.5% at 77 and zero after 98 days. A similar decrease in regeneration capacity was observed when HG2 was maintained as a solid callus. Clone HG2 is expected to provide the basic material for future experiments on variant selection.