Direct modeling methods for air-cored pulsed alternators

A railgun launcher requires very high-current pulsed power over the period of a few milliseconds. For laboratory systems, capacitor banks have traditionally been used to provide this energy, but field applications require a system with significantly higher energy storage density. Rotating machines that store the energy in the form of rotational kinetic energy and can quickly convert it to high-current electrical energy have been designed and built. These low-impedance multiphase, multipole synchronous generators are referred to as pulsed alternators. The AC output of the pulsed alternator is rectified to provide DC to power the railgun, and the design of the rectifier set and control circuitry is very dependent on the alternator characteristics. To facilitate the design and evaluation of the overall pulsed power system, a modeling tool which accurately represents the performance of the pulsed alternator while allowing easy changes to the external circuitry and controls is needed. This paper describes a manner in which these pulsed alternators can be accurately modeled. The validity of the model is established by comparing it to experimental data gathered from the "Subscale" alternator built by the Center for Electromechanics at The University of Texas under the Focused Technology Program (FTP).