This paper details the testing of a commercially available gate turn-off thyristor (GTO) for application in inductive-store power supplies. GTOs have been used as a component of inductive-store systems directly and as part of compound switches. These GTOs are generally available commercially and typically have extensive datasheets. However, the inductive-store application differs significantly from conventional switching applications, which significantly reduces the utility of the datasheets; GTOs are typically used at 100-1000 Hz in a fairly continuous manner, whereas in an inductive-store system, a GTO may be conducting for a relatively long time before doing a single turn off.

A large-caliber railgun was developed to demonstrate the supersonic launch of 120 mm projectiles. A trade study that evaluated over 70 different railgun configurations and geometries resulted in the selection of a high-inductance-gradient, multi-turn configuration as the best overall choice. Subscale tests were performed on both the railgun and launch package configurations. A full-scale laboratory system was installed that included a dedicated high-current, large-caliber breech and gunline. A full-scale launcher was successfully tested to beyond the design conditions.

Summary form only given. This paper reports on the design and fabrication efforts of a supersonic, high-mass electromagnetic launcher. The program goal was to efficiently accelerate an existing M933/934 mortar round to over 400 m/s. The basic electromagnetic architecture chosen was a railgun, with a detailed system study undertaken to determine the optimal railgun configuration. Operational limits required that the overall launch package have a mass of less than 18 kg and a length of less than one meter. The peak acceleration was required to be less than 10 kG, and no launch package components could be discarded in flight. In addition, the program required a laboratory demonstration, which when coupled with the schedule and budget constraints, required that the existing IAT electromagnetic launch facility (ELF) be capable of providing the prime power.

The Institute for Advanced Technology is using a pair of physical scale model alternators as counter-rotating pulsed alternator simulators. These alternators have similar but not identical electrical characteristics. The original goal was to use these alternators to simulate a two-machine pulsed alternator system to study thyristor converter operation, with the two machines electrically connected at the output (dc side) of the thyristor (SCR) converter. Additional experiments were also run with the two alternators electrically connected at the input (ac side) of the thyristor converter. In the experiments, control algorithms were developed to test self-excitation and to discharge pulsed energy into various types of loads-resistive, inductive, and capacitive-to evaluate energy sharing from each alternator. Negative resistance circuits were implemented to adjust the field winding time constant of each alternator to achieve correct resistance/reactance ratio of full-scale pulsed alternators and to achieve equal energy discharge from each alternator

Pulsed power supplies for electromagnetic launch have unique requirements, including very low impedance, relatively long pulse discharge times, and high stored energy. The three primary types of pulsed power systems for electromagnetic launch have been capacitive, inductive, and rotating machine. This paper describes recent results in the design, construction, and testing of a pulsed power system based on an inductor that is charged by batteries.

Electromagnetic launchers typically feature a containment structure around the rails that is fabricated using high-strength stainless steel laminations. Eddy currents induced in these laminations reduce the propulsive force in the launcher, leading to a reduction in incremental inductance-a fundamental railgun design parameter. Thus, designers need a method to simulate the effect of the laminated containment structure on this parameter. Using finite-element (FE) analysis to model individual laminations is likely to be counterproductive; an impossibly large number of elements would be required to model the laminations, and the insulating layers between them, for the entire railgun. Instead of modeling the physical structure of the laminated containment, it is more productive to model the effect it has on magnetic fields around the armature. The basic idea is to replace the laminated containment material with anisotropic material with different properties in the longitudinal and transverse directions. Both electrical conductivity and magnetic permeability of the containment structure will affect the magnetic field around the armature, and both these properties can be represented by an anisotropic model for the bulk. The phenomenological model discussed in this paper is designed to find the magnetic fields and currents at the sliding armature, so that L' can be calculated using readily available commercial FE codes

Advances in high-power-density batteries have rekindled interest in using inductive store as a pulse compression system. Although these batteries are considered very power dense, they lack over an order of magnitude of power density to drive a deployable electric gun. However, one can add an inductive circuit to a battery bank to make a hybrid system that has a much higher power density than batteries alone. A battery-inductor hybrid pulsed-power supply boasts several advantages over pulsed alternators, as inductors are static and relatively easy to cool. Inductors are potentially more energy dense than capacitors, making a battery-inductor hybrid pulsed-power supply an attractive alternative to capacitor-based pulsed-power supplies. The opening switch has been a major obstacle in previous inductive store projects, but in simulation, a new circuit topology-the Slow Transfer of Energy Through Capacitive Hybrid (STRETCH) meat grinder-greatly attenuates the problem. This paper discusses the design, construction, and testing of a small-scale STRETCH meat grinder system, which was successfully used to power a miniature railgun

Pulsed alternators configured as counter-rotating pairs are being considered as a potential pulsed-power source for electromagnetic launchers. The Institute for Advanced Technology is interested in studying the electrical and mechanical characteristics of such a pair of counter-rotating pulsed alternators; however, implementation and experimentation have only been attempted on a single subscale alternator machine that requires extensive laboratory support for operation. As a first step toward testing the electromechanical effects of counter-rotating alternators, two iron-core wound field alternators driven by dc motor prime movers were obtained and implemented as a scale model pulsed-power source simulator. These alternators were originally designed and fabricated at the Massachusetts Institute of Technology as physical scale models of 900-MVA utility alternators, which exhibit the same per-unit reactance and time constants as the full-scale machines. A digital signal processor was integrated into a real-time control system designed to maintain the two generators as an electrically coupled, counter-rotating generator pair. This paper documents the control system design, the incorporated control algorithm, and the automated test setup implemented for experimental data collection

The vast majority of all operational railguns in the world employ a metallic containment housing. Often composed of thousands of precision sheet metal laminates to prevent induced eddy currents, the launchers are labor intensive to build. The backbone railgun provides a monolithic metallic containment structure. Induced eddy currents are inhibited by the introduction of a large number of slits along the length of the launcher that achieve an effect analogous to traditional laminates. It is anticipated that the machining of slits from a monolithic launcher will lend itself to factory automation far more so than assembling a full length launcher from thousands of individual metal laminates. The principal advantages are: 1) elimination of stack-up tolerances; 2) producibility; and 3) stiffness. This paper will refine the concept and include an assessment of its ability to achieve magnetic transparency relative to traditional designs.

In order to evaluate the size and weight of a tactical electromagnetic launch system, one needs to estimate the contribution of the pulsed alternator power supply. This paper develops a set of equations that shows that the energy delivery of a pulsed alternator feeding an electromagnetic launcher is governed by a rather simple set of parameters based upon geometry, internal magnetic energy, and rotational speed.

Rotating machinery can be used to store kinetic energy and convert it to high current electrical energy in the millisecond time frame required by pulsed loads such as electromagnetic launchers. Machines used in these applications, called pulsed alternators, often require nonstandard features, such as low impedance, more than three phases, or compensating windings inside or conductive shields outside the machine. Design and analysis of systems utilizing pulsed alternators require accurate transient modeling. We present a direct and quadrature (DQ) representation of the system dynamics for nonstandard electric machines used in pulsed power applications, which can be used to construct efficient simulation models. Simulation results using the resulting model are presented and compared to an existing model, which has been validated with test data.

The slow transfer of energy through capacitive hybrid (STRETCH) meat grinder is an inductive- capacitive current multiplication circuit that reduces switching requirements and achieves a high degree of current multiplication while possessing an energy density approaching that of a purely inductive system. Initially, the STRETCH meat grinder operates like a single-stage meat grinder; it increases the current through an inductor by switching out a coupled inductor. However, during switching in generic meat grinder circuits, leakage flux caused by imperfect coupling and the sudden change in current induces a voltage across the opening switch well beyond what modern solid-state switches can handle. The STRETCH meat grinder mitigates these problems by using a capacitor to recapture the energy in the leakage flux and to slow down the turnoff of current in one of the inductors. The energy from the leakage flux is then used to reverse the current on the turned-off inductor, thereby further increasing the current multiplication. A system comprising several STRETCH meat grinders in parallel can develop currents in the mega-ampere range without exceeding the capabilities of solid-state switches. Such a system could be used to power a railgun.

Proposed electromagnetic launch systems using pulsed alternators usually employ a phase-angle-controlled thyristor converter to supply DC to the railgun launcher. By carefully choosing the firing angles of the individual thyristors, the system designers can control shape of the current pulse delivered to the launcher, thereby controlling projectile acceleration and magnetic energy recovery from the launcher after muzzle exit. This paper describes a simple method for determining the required phase angles for a specified launch current waveform, using a simplified equivalent controlled DC source model for the pulsed alternator and converter system. Once a desired current profile is chosen to deliver the required action to the projectile, the railgun equations are used to determine the required breech voltage profile. The thyristor firing angle vs. time to produce this breech voltage is then calculated from the equivalent DC source model. Improvements to the basic model incorporating field current decay and rotor speed reduction with time are discussed. The method has been embedded in a Mathcad/spl trade/ worksheet. Results from the simplified model show good agreement when compared to a detailed Saber/spl trade/ system simulation.

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 that energy 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. 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.The direct-quadrature, or Park's, transformation is commonly used to model synchronous generators for simulation, but such models are better suited for modeling disturbances around a steady-state operation point in a power system. A pulsed alternator may deliver half of its stored rotational energy in just a few mechanical cycles. This results in very high discharge torques and large armatures reactions that are difficult for many commercial simulators and synchronous generator models to handle properly. In addition, the transient nature of the discharge can require that electromagnetic interaction with nonwinding structures in the generator be modeled to accurately predict the performance of the system.This paper describes a manner in which these pulsed alternators can be accurately modeled. The simulation platform SABER was chosen because of the robust modeling engine, the ease of integrating mechanical components, and the large library of existing models for a wide rang e of electrical components. 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.

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).

This paper presents an evaluation of the capabilities of the switched reluctance motor drive particularly in small integral-horsepower sizes, and discusses some of its special features. The simplicity of construction of the rotor, together with certain advantages in the power circuit such as unipolar operation and the independence of the phases, are described along with some of the important performance parameters, which are compared with those of typical induction motor drives. It is shown that the ruggedness and simplicity of the SR drive are accompanied by a performance "profile" that matches that of modern induction motor drives in torque per unit volume, efficiency, converter volt-ampere requirements, and other parameters. A comparison of three SR motors, including one low-inertia design and one with two stator teeth per pole, shows torque/inertia ratios several times greater than for induction motor drives.