Some benefits of pulsed alternators as electromagnetic gun power supplies in power systems for future electric ship

An electromagnetic gun provides a new component to be integrated into the power system of an electric ship.  Electromagnetic guns have been fired successfully using either capacitors, inductors, or rotating machines to store the energy for the shot.  Because capacitors trail rotating machines by more than an order of magnitude in the stored energy density, fielded systems will likely use rotating machines even though other approaches are used in laboratory experiments.  An interesting topology for the power supply is a set of pulsed alternators with sufficient energy stored in the kinetic energy of the rotors to power a sequence of shots.  In this configuration, when no shot is required, which historically has been most of the life of the system, the machine topology is analogous to that of a flywheel battery used to provide ride-through capability and improve power quality in land-based power systems or to provide load leveling in hybrid vehicles.  This similarity raises the possibility that the power supply could be designed to serve multiple roles under conditions of ship operation.  The conceptual design of such a power supply of eight alternators storing a total of 800 MJ has been completed.  Megawatt-level motor-generators operating at speeds up to 15,000 rpm have been designed, constructed, and tested.  Simulations of future electric ship power systems show the utility of this storage for load leveling.  In addition, these components provide storage for an uninterruptible power supply for critical ship loads in the case of the loss of a generator.  An important unresolved problem is the design of bearings that will operate at high speeds reliably for long periods and survive the high levels of shock and vibration that will be encountered.  The paper, “Some benefits of pulsed alternators as electromagnetic gun power supplies in power systems for future electric ships,” by R. E. Hebner , J. A. Pappas, J. R. Kitzmiller, K. R. Davey, J. D. Herbst, A. Ouroua, and J. H. Beno was presented at the IMAREST Engine as a Weapon II International Symposium in London, UK, in December 2006.

For further information, please contact Robert Hebner.

A New Strategy for Representation and Control of Self-Contained Power Systems

Power systems on naval vessels and airplanes are good examples of self-contained power systems.  State of the art LEM modules and voltage sensors provide real time current and voltage data.  This paper shows how that information can be used to construct dynamic equivalent impedance representations of the system discretized into key trunk lines.  Error analysis indicates that the algorithm performing this representation can be updated in one fifth of a cycle if the signal to noise data ratio is 5% or less.  The magnitude of the equivalent impedance is sufficient to determine when fault control on either end of the trunk line is required.  These same equivalent impedances can be used to determine the best switch configuration to maximize load power while minimizing transmission loss subject to line load capability.  In the paper, “A new strategy for representation and control of self-contained power systems,” by Kent R. Davey and Robert E. Hebner and published in the IEEE Transactions on Power Delivery, vol. 21, no 3, July 2006, the accuracy of the equivalent impedance approach is assessed for transients with active and passive loads.

For further information, please contact Kent Davey.

High Speed Generator Trade Study

The paper, “High Speed Generator Trade Study,” by Kent Davey, John Herbst, James Bravo, Reg Ricket, and Bruce Gamble, was presented at the ASNE Electric Machines Technology Symposium in May 2006. The paper compares high temperature superconducting (HTS), permanent magnet, and wound rotor designs of 5, 10, and 14 MW generators driven at 16,000 rpm, 7,000 rpm, and 7,000 rpm machines, respectively. The purpose was to identify power density trends vs. rating among the three options studied. Parametric analysis was used to design electrical generators optimized by weight. Different cooling strategies were considered to increase the slot current density. The results suggested that permanent magnet machines are best for weight at lower powers (< 8 MW) and higher speeds (> 10,000 rpm), but that wound rotor and HTS machines show superior power/weight ratios at higher power (> 8 MW) and lower speed (< 10,000 rpm). The HTS designs were lightest above 8 MW.

For further information, please contact Kent Davey.

A New Strategy for Management and Reconfiguration of Self-Contained Power Systems

Power systems on naval vessels and airplanes are good examples of self-contained power systems.  These types of systems are useful for testing reconfiguration, particularly ones that might be implemented continuously, not just under compromised conditions.  Determining the best operating condition in real time is challenging, since it discourages stochastic approaches.  A fixed grid representation of the dynamic loads is recommended, employing a phasor algorithm to update the load impedances.  A new subspace approach for solving the reconfiguration is presented and compared to branch and bound algorithms in the paper, “A new strategy for management and reconfiguration of self-contained power systems,” by Kent R. Davey and Robert E. Hebner and published in the IEEE Transactions on Power Delivery, vol. 21, no. 3, July 2006.  In the paper, reconfiguration is studied for a test system with 16 million switch options.  Also discussed is how this information can be used in the design of the power grid a priori.

For further information, please contact Kent Davey.