Some Benefits of Pulsed Alternators as Electromagnetic Gun Power Supplies on Power Systems for Future Electric Ships

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.