Publications

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Power systems with highly flexible architectures (i.e. permitting many configurations) may allow for more economic operation as well as improved reliability and resiliency. The greater number of configurations enable optimization for attaining the former benefit and redundancy for achieving the latter. Flexibility is of great importance in electric ship power systems wherein the system must ensure delivery of power to vital loads. The United States (US) Navy is currently investigating new architectures that enable a greater number of interconnection permutations. Among the new features considered are generators that may supply two buses; this may be done using conventional (single winding set) generators and two rectifiers or a dual wound machine with two rectifiers. In systems supplied by dual-wound machines, buses may not be tied directly but are linked dynamically through the shared generator dynamics. In systems with conventional generation supplying two rectifiers, the two buses are tied through a common AC bus supplying both rectifiers. This paper presents a comparison of these two approaches of supplying two buses from one generator; the evaluation considers issues associated with dynamic coupling through these two candidate architectures, including the coupled response due to faults and systems with pulsed loads. Results are based on analysis, simulation results, and hardware experiment.

This paper describes the design of a very high power density inverter drive module using aggressive high-frequency design methods and multi-objective optimization tools. This work is part of a larger effort to develop electric drive designs with >97% efficiency, power densities of 100 kW/L for the power electronics, and with predicted reliable operation to 300, 000 miles. The approach taken in this work is to develop designs that utilize wide band gap devices (SiC or GaN) and ceramic capacitors to enable high-frequency switching and a compact integrated design. The multi-objective optimization is employed to select key parameters for the design.

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This paper evaluates the performance of a novel nano-composite core inductor. In this digest, a brief explanation of the superparamagnetic magnetite nanoparticle core is given along with magnetic characterization results and simulated design parameters and dimensions. A nearly flat relative permeability (μr) of around 5 is measured for the magnetic material to 1 MHz. A synchronous buck converter with nano-composite inductor was constructed and evaluated; the converter demonstrates a 1% improvement in conversion efficiency at higher currents (4% reduction in electrical losses), compared to an identical circuit with a benchmark commercial ferrite inductor.

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Forced oscillations in power systems are of particular interest when they interact and reinforce inter-area oscillations. This paper determines how a previously proposed inter-area damping controller mitigates forced oscillations. The damping controller modulates active power on the Pacific DC Intertie (PDCI) based on phasor measurement units (PMU) frequency measurements. The primary goal of the controller is to improve the small signal stability of the north south B mode in the North American Western Interconnection (WI). The paper presents small signal stability analysis in a reduced order system, time-domain simulations of a detailed representation of the WI and actual system test results to demonstrate that the PDCI damping controller provides effective damping to forced oscillations in the frequency range below 1 Hz.

The U.S. Navy is investing in the development of new technologies that broaden warship capabilities and maintain U.S. naval superiority. Specifically, Naval Sea Systems Command (NAVSEA) is supporting the development of power systems technologies that enable the Navy to realise an all-electric warship. A challenge to fielding an all-electric power system architecture includes minimising the size of energy storage systems (ESS) while maintaining the response times necessary to support potential pulsed loads. This work explores the trade-off between energy storage size requirements (i.e. mass) and performance (i.e. peak power, energy storage, and control bandwidth) in the context of a power system architecture that meets the needs of the U.S. Navy. In this work, the simulated time domain responses of a representative power system were evaluated under different loading conditions and control parameters, and the results were considered in conjunction with sizing constraints of and estimated specific power and energy densities of various storage technologies. The simulation scenarios were based on representative operational vignettes, and a Ragone plot was used to illustrate the intersection of potential energy storage sizing with the energy and power density requirements of the system. Furthermore, the energy storage control bandwidth requirements were evaluated by simulation for different loading scenarios. Two approaches were taken to design an ESS: one based only on time domain power and energy requirements from simulation and another based on bandwidth (specific frequency) limitations of various technologies.

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This paper describes the design and implementation of a proof-of-concept Pacific dc Intertie (PDCI) wide area damping controller and includes system test results on the North American Western Interconnection (WI). To damp inter-area oscillations, the controller modulates the power transfer of the PDCI, a ±500 kV dc transmission line in the WI. The control system utilizes real-time phasor measurement unit (PMU) feedback to construct a commanded power signal which is added to the scheduled power flow for the PDCI. After years of design, simulations, and development, this controller has been implemented in hardware and successfully tested in both open and closed-loop operation. The most important design specifications were safe, reliable performance, no degradation of any system modes in any circumstances, and improve damping to the controllable modes in the WI. The main finding is that the controller adds significant damping to the modes of the WI and does not adversely affect the system response in any of the test cases. The primary contribution of this paper, to the state of the art research, is the design methods and test results of the first North American real-time control system that uses wide area PMU feedback.

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The purpose of the International Technology Roadmap for Wide-Bandgap Power Semiconductors (ITRW) Materials and Devices Working Group, which considers the materials science of Wide-and Ultra-Wide-Band-Gap (WBG and UWBG) semiconductors, in addition to device design, fabrication, and evaluation, is to formulate a long-term, international roadmap for WBG and UWBG materials and devices, consistent with the packaging and applications working groups of ITRW. The working group is co-chaired by Victor Veliadis (primarily representing silicon carbide (SiC) and related materials) and Robert Kaplar (primarily representing gallium nitride (GaN) and related materials, as well as emerging ultra-WBGs) and is split into four sub-working-groups, which are: 1) SiC materials and devices (co-chairs Jon Zhang and Mietek Bakowski). 2) Lateral GaN materials and devices (co-chairs Sameh Khalil and Peter Moens). 3) Vertical GaN materials and devices (co-chairs TBD). 4) Emerging UWBG materials and devices (co-chairs Mark Hollis). The first two subgroups represent technology that is far more mature than that of the latter two, and devices are available as commercial products in power applications. The primary focus of this article will be on developments in subgroups 1 and 2, with only brief descriptions of the latter two sub-groups, including future activities as they mature technologically.

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