Electric Ship Power System

Recognizing the importance of electric ships and the myriad of technical challenges they present, the University of Texas at Austin, with seed funding from the Office of Naval Research, established a virtual electrical ship research and development center.  The reason for the virtual center is that the complex challenges of the future require multidisciplinary solutions.  The virtual center contains staff members from Electrical Engineering, Mechanical Engineering, and two research centers who work collaboratively with a number of other universities and with industry.  This program has two anticipated significant outcomes.  At the system level, the first is to develop a comprehensive set of modeling approaches that guide the evolution of electric ship power systems.  The second is an approach to the replacement of the hydraulic system on current ships with electrical actuators on future ships.  This work was reported in a paper, “Electric Ship Power System – Research at the University of Texas at Austin,” by R. E. Hebner, that was presented at the 2005 IEEE Electric Ship Technologies Symposium in July.  For further information, contact R. Hebner.

Reconfiguration: A Tool for Designing New Ships

The objective of reconfiguration is to re-route power during failure or compromised conditions to improve fight through capability and survivability.  Rapid algorithms for the task may serve the dual purpose of managing power flow under dynamic load change.  Among the critical constraints of power redirection is the line current rating.  Reconfiguration algorithms serve an equally useful task in system grid design.  An exhaustive search optimization routine can be used to specify the grid layout necessary to guarantee 100% performance in the face of single and multiple line loss.  A genetic optimization routine is employed to determine required line rating and switch configuration during generator loss to satisfy critical load demands.  The combination of these tests results in line current rating and switch locations necessary for reliable ship operation for the least cost.  This work was reported in a paper, “Reconfiguration: A Tool for Designing New Ships,” by Kent R. Davey and Robert E. Hebner, that was presented at the 2005 IEEE Electric Ship Technologies Symposium in July. For further information, contact Kent Davey.

Electric Ship Power System Integration Analyses Through Modeling and Simulation

The Center for Electromechanics is engaged in the development of a comprehensive power system model to address several challenging issues facing the development of a viable and effective integrated power system architecture for future naval platforms.  The power system under consideration reflects the notional electric ship power system architecture and is developed in the Matlab/Simulink® environment.  System components, such as motors and generators, are modeled using parameters based on actual machine design and analysis work performed at UT.  Simulation results of models, including permanent-magnet propulsion motors and generators with simple reconfiguration scenarios simulating loss and recovery of power to propulsion and vital loads, were reported in a paper, “Electric Ship Power System Integration Analyses through Modeling and Simulation,” by A. Ouroua, L. Domaschk, and J. H. Beno, that was presented at the 2005 IEEE Electric Ship Technologies Symposium in July. For further information, contact A. Ouroua.

Characterization of Power Losses in Soft Magnetic Materials

The power density of electric machines may be increased by designing for operation at higher rotation speeds and temperatures.  Such operation increases the mechanical stresses, frequency, and temperature attained in the soft magnetic materials.  Increased power losses in the magnetic material can be quantified empirically by controlled hysteresis experiments allowing improved simulation of machine operation.  Standard hysteresis experiments operate at ac excitation, room temperature, and no applied mechanical stress.  This is the extent of variables considered by some electromagnetic simulation programs.  The involved research community is currently developing semi-empirical models that account for additional power losses due to rotation, pulse waveform modulation, compressive stress, and residual forming stresses and/or machining damage.  Concurrently, models also account for reduced power losses due to tensile stress and increased temperature.  A paper discussing a model for each environmental variable using the performance of Hiperco®50HS (a cobalt-iron-vanadium steel) as an example, “Characterization of Power Losses in Soft Magnetic Materials,” by Aleta T. Wilder, was presented at the 2005 IEEE Electric Ship Technologies Symposium in July.  For further information, contact A. Wilder. For further information, contact A. Wilder.

Materials for Advanced Electric Machines

Materials behavior, along with machine design, controls the performance of the electric machine.  Advanced electric machines are placing increased demands on materials behavior especially to achieve power density, efficiency, and endurance.  For the electric ship, such advanced electric machines include actuators, motors, generators, certain energy storage systems, electric clutches and brakes, and specialized machines for weaponry.  Small engineering refinements from practice are often inadequate for the advanced electric machine systems and the associated materials utilized in these machines to meet performance goals.  A method for directing appropriate attention to materials requirements based on the machine performance goals is needed.  A paper presenting a method for prioritizing materials issues based on ten machine performance categories, “Materials for Advanced Electric Machines: An Overview,” by Aleta T. Wilder, was presented at the 2005 IEEE Electric Ship Technologies Symposium in July. For further information, contact A. Wilder.