AC microgrids are a convenient approach to integrating distributed energy systems with utility power systems. On the other hand, DC micro-grids can lead to more efficient integration of distributed generation. They are the preferred topology for present shipboard, aircraft and automotive power systems and hold promise for future environmentally friendly office buildings, homes, rural areas and industrial power parks. However, standards, guidelines, practical experience and cost effective implementations for DC system protection are well behind practices in AC system protection. This paper presents a comprehensive overview of the body of research on protection of DC micro-grids, presented with a goal of identifying and advancing the field. The paper presents a discussion of the current status of dc micro-grid protection, including the use of electro-mechanical circuit breakers, solid state circuit breakers, protective system design, ground fault location and fault isolation.

The Status of DC Micro-Grid Protection

The evolution of the use of electricity in marine vessels is presented and discussed in this paper in an historical perspective. The historical account starts with its first commercial use in the form of light bulbs on the SS Columbia in 1880 for illumination, going forward through use in hybrid propulsion systems with steam turbines and diesel engines and then transitioning to the present with the first fully electric marine vessel based entirely on the use of batteries in 2015. Electricity use is discussed not only in the light of its many benefits but also of the challenges introduced after the emergence of the marine vessel electrical power system. The impact of new conversion technologies like power electronics, battery energy storage, and the dc power system on overall energy efficiency, power quality, and emission level is discussed thoroughly. This paper guides the reader through this development, the present and future challenges by calling attention to the future research needs, and the need to revisit standards that relate to power quality, safety, integrity, and stability of the marine vessel power system, which are strongly impacted by the way electricity is used in the marine vessel.

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Past, Present, and Future Challenges of the Marine Vessel’s Electrical Power System

Tomorrow's marine electrical systems will be profoundly different from today's systems. Power electronics is making major impacts on virtually every marine system including propulsion, power distribution, auxiliaries, sonar, and radar. Newly emerging materials, components, and system concepts (such as wide band-gap materials, silicon-carbide-based power semiconductor devices, power electronics building blocks (PEBBs), and integrated power systems) are, and will continue, enabling future marine systems as different from today's systems as steam ships were to sailing ships. However, these enabling technologies and concepts are not well known and have been difficult to understand. This paper will introduce these new concepts and technologies, identify potential impacts, and explore new design methods to simplify marine electrical system development.

Power electronics and future marine electrical systems

In multi-module power electronics systems, especially DC distributed power systems, the small-signal stability issues are often dealt with by employing Middlebrook's impedance criterion. However, for on-line system stability margin monitoring, directly measuring impedance of the source and load subsystems then making quantitative comparisons is too complicated and difficult. This paper proposes practical and simple methods, which involve applying current or voltage perturbation to the dc side of distributed power systems then only measuring the amplitude of two currents or voltages in order to monitor the stability margin. For both methods (current perturbation and voltage perturbation), an implementation approach that does not employ external voltage or current perturbation source is also presented. All these methods and approaches are equivalent to the impedance measuring and comparing method based on the impedance criterion with different forbidden regions. A comparative evaluation of each method and its corresponding implementation approach is provided.

Stability margin monitoring for DC distributed power systems via perturbation approaches

Tomorrow's marine electrical systems will be profoundly different from today's systems. Power electronics is making major impacts on virtually every marine system including propulsion, power distribution, auxiliaries, sonar, and radar. Newly emerging materials, components, and system concepts (such as wide band-gap materials, silicon-carbide-based power semiconductor devices, power electronics building blocks and integrated power systems) are, and will continue, enabling future marine systems as different from today's systems as steam ships were to sailing ships. However, these enabling technologies and concepts are not well known and have been difficult to understand. This paper introduces these new concepts and technologies, identify potential impacts, and explore new design methods to simplify marine electrical system development.

Power Electronic Building Blocks (PEBBs) are power processors. A PEBB is not a specific semiconductor material, not a device, nor a circuit topology. It is the search for the common electrical, mechanical and thermal denominators of all these, allowing integration of all these technologies. It is not; "one size fits all". There will be several blocks that will fit together to perform the majority of everyday power electronic jobs. Like a set of children's interlocking blocks, PEBBs will be a rational and simple set of blocks and procedures that most any designer or architect can use to build electrical systems. The Office of Naval Research (ONR) is developing Power Electronic Building Blocks to achieve: increased power density, "user friendly" design ("plug and play" power modules), and multi-functionality. Digital controls, integrated with higher frequency and more robust power circuits, enable modular power systems with lower size, weight, and cost-while increasing performance. Although the day when solid-state will replace tubes in high-power modulator applications is still in the future, many near-term opportunities exist for PEBBs and associated technologies. This paper presents requirements, opportunities and issues for standardized power modules. First, an overview of the PEBB program is given. Then, opportunities are examined for technologies developed by the PEBB program.

T. Ericsen

Papers

Power Electronics Building Blocks and potential power modulator applications