Single and multiphase compulsator system architectures: a practical comparison

The Center for Electromechanics at the University of Texas at Austin (UT-CEM) has designed, built, and tested three generations of iron-core and air-core compensated pulsed alternators (CPA). These include the iron core, small caliber, cannon caliber, and model scale compulsators. Early CPA were single-phase machines that were optimized for a specific load and desired performance. The most recent machine, the model-scale CPA, is a multiphase alternator coupled to the load through a rectifier. This paper includes a discussion of the requirements and capabilities of both single-phase and multiphase systems, a point design for each system type, and a comparison of system performance in driving a cannon caliber launcher.

I. Introduction

Compensated pulsed alternators (also called compulsators) are high-performance generators designed to discharge into a short circuit. Compulsator (CPA) operation requires that the magnetic coupling between armature and field windings be optimal and that a compensating winding act to compress the flux between coils, thereby lowering the internal impedance of the generator. The compensating function may be fulfilled by the armature winding, the field winding, or an additional shorted winding. CPA may have ferromagnetic or nonferromagnetic materials in the flux path; a machine without iron in the flux path is an air-core CPA. The peak flux density in a typical air-core CPA exceeds 2 T. The need to remove iron from the flux path in high-field alternators has led to the use of advanced composite materials in both the rotor and the stator. Fig. 1. Principal hardware components for a compulsator railgun system.