13 research outputs found
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25 GW Homopolar Generator Experiment
Early in the design iterations for the Balcones 60 MJ power supply different options were considered, from a single machine to modular homopolar generators (HPGs).[1] A multiple machine option was chosen to provide greater system flexibility. Envisioned uses for the power supply were to weld up to 100 in.2 of metal, heat a 100 lb steel billet to forging temperature in 2 to 4 s, and conduct high level electromagnetic gun experiments.[2] A study involving detailed computer optimization compared drum type HPGs to disk type machines. For fixed location (such as large proof of principle laboratory experiments) the higher energy transfer efficiency and lower cost perjoule delivered made the drum configuration more attractive. The compact disk design was better for mobile applications where minimum mass is the primary consideration.[3] The six drum HPGs installed in the underground hexagonal pit in the Balcones lab are shown in figure 1.Center for Electromechanic
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Pulsed Power Accelerators at CEM-UT
An overview of four accelerator programs utilizing pulsed power is presented. The goals of each project, a description of the power supplies and launchers utilized and test results from each program are provided. The four projects presented illustrate a variety of uses for electromagnetic (EM) launchers and the potential advantages and disadvantages of four different launcher systems. Included in the paper are micrometeorite impact studies of 50 to 500 μm diameter glass beads accelerated up to 11 km/s with plasma armatures and 2.5- kg solid armature packages launched at 2.6 km/s (a record 8.1 MJ of muzzle energy). A compact rep-rateable augmented rail launcher and compulsator system weighing less than 1,100 kg is also described. Finally a skid mounted rep-rateable launcher system capable of providing 9 MJ of muzzle energy is discussed.Center for Electromechanic
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Operating Modes for Compulsator Based Electromagnetic Launcher Systems
The compensated pulsed alternator (compulsator) is a versatile power supply capable of interfacing with the electromagnetic launcher in various ways. The method that has been explored at length with several systems is the single phase option. Several variants of this option, some using advanced pulse shaping techniques, have been discussed in prior publications [I-3]. Besides this basic single pulse method of operating there are several other methods each with its pros and cons. The multi-phase option is discussed in this paper. Within the broad class of multi-phase systems there are further sub-classes, namely alternating current drive and unidirectional current drives. Thus the branching of these operating modes gives rise to a variety of operating modes. Each one of these operating modes is described and simulation results are presented.Center for Electromechanic
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Active Magnetic Bearings for Energy Storage Systems for Combat Vehicles
Advanced energy storage systems for electric guns and other pulsed weapons on combat vehicles present significant challenges for rotor bearing design, Active magnetic bearings (AMBs) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favorably integrate into high-speed flywheel systems. The Department of Defense Combat Hybrid Power Systems (CHPS) program serves as a case study for magnetic bearing applications on combat vehicles. The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 318 kg (700 lb), 20000 rpm rotor. To minimize CHPS flywheel size and mass, a topology was chosen in which the rotating portion of the flywheel is located outside the stationary components. Accordingly, magnetic bearing actuators are required which share this configuration. Because of inherent low loss and nearly linear force characteristics, UT-CEM has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance, a nonrotating bearing test fixture was designed and built which permits measurement of static and dynamic force. An AMB control system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. This paper discusses bearing system requirements, actuator and controller design, and predicted performance; it also compares theoretical vs. measured actuator characteristicsCenter for Electromechanic
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Electromagnetic Force, Jerk, and Electric Gun Projectile Design
As railgun projectiles have become more sophisticated, attention is being given to railgun produced electromagnetic forces that affect the mechanical loading of the projectile. The rate at which a launch package is accelerated directly relates to the stresses developed in the projectiles structural members. Acceleration rate is defined as jerk. This paper will define jerk in terms of electromagnetic parameters and give simple examples of stress amplification with increasing acceleration rate. For a given barrel caliber and length, railgun and projectile structural limitations produce a family of curves which define a range of allowed muzzle energies. Maps of ideal performance will be presented based on idealized current waveforms modified to observe railgun and projectile structural limitations. Once an acceptable current waveshape is identified, the pulsed power source must be modified to produce the required output. In a capacitor system, the series Inductance may be designed to produce. the appropriate waveshape; in the compulsator system, the inductance variation and initial firing angle of the machine may be adjusted to meet current rise requirements, and; in the railgun system driven with inductive stores, the opening switch function has to be modified to produce the desired acceleration profile. The second part of this paper describes a modification to explosive opening switches which allows control of the developed voltage of the switch and therefore, the rate of rise of current in the railgun. Experimental data demonstrating this capability on the Balcones 60 MJ power supply will be presented.Center for Electromechanic
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BUS High Current Battery Model
An empirical model for voltage and equivalent series resistance (ESR) has been developed for lead acid batteries used as a pulsed power source. During the design of the battery upgraded supply (BUS) for Eglin Air Force Base, the Center for Electromechanics at the University of Texas at Austin (CEM-UT) developed a model for the batteries to be used in this system. BUS is a 5 MA, 500 MJ inductive power supply charged by batteries for use as a railgun power supply. A series of tests was performed to determine the driving voltage and ESR of the batteries for discharge times from 2 to 10 s and current levels from 500 to 2500 A. A model for voltage and ESR was obtained from these tests. The methods used and sample data from the tests are presented. The main factors affecting battery voltage and ESR are discussed, and the models developed for the batteries tested are described. It is concluded that the proposed empirical model can be used to predict the performance of Pulsar batteries as long as the currents are around 500 to 2500 A and the timeframes are from 2 to 10 sCenter for Electromechanic
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Design and Testing of a Flywheel Battery for a Transit Bus
The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed and tested a flywheel energy storage system conventionally referred to as a flywheel battery (FWB) for power averaging on a hybrid electric transit bus. The system incorporates a high speed (40,000 rpm) 150 kW permanent magnet motor generator with magnetic bearings to levitate a 2 kWh composite flywheel. This paper summarizes: design goals, required operating parameters, system design, analysis completed prior to fabrication, and initial performance testing completed in the laboratory. The paper includes information on the motor/generator, power electronics, magnetic bearing sensors and controls, and FWB subsystems (including containment). Finally, recommendations for continued testing are made along with recommendations for improvements to the existing design.Center for Electromechanic
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A Study of Operating Modes for Compulsator Based EM Launcher Systems
The compensated pulsed alternator (compulsator) is a versatile power supply capable of interfacing with the electromagnetic launcher in various ways. The method that has been explored at length with several systems is the single phase option. Several variants of this option, some using advanced pulse shaping techniques, have been discussed in prior publications. Besides this basic single pulse method of operating there are several other methods each with its pros and cons. The multiphase option is discussed in this paper. Within the broad class of multi-phase systems there are further sub-classes, namely alternating current drive and unidirectional current drives. Thus the branching of these operating modes gives rise to a variety of operating modes. Each one of these operating modes is described and simulation results are presentedCenter for Electromechanic
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Inside-Out Configuration Active Magnetic Bearing Actuators
The University of Texas Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 700 lb (318 kg), 20,000 rpm rotor, under the sponsorship of the Department of Defense Combat Hybrid Power Systems (CHPS) program. Because this machine incorporates an unusual inside-out topology (i.e., the rotating portion of the flywheel is located outside the stationary components), unique inside-out configuration magnetic bearing actuators are required. Permanent magnet bias bearings were chosen for this application because of inherent low power requirements, low power losses, and nearly linear current stiffness and positional stiffness. To verify performance, a bearing test fixture was designed and built which permits static and dynamic force measurement. This paper discusses bearing requirements, actuator design, predicted performance, and compares theoretical versus measured bearing characteristics. A companion paper discusses control issues for this unique magnetic bearing system.Center for Electromechanic
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Control System for Inside-Out Configuration Magnetic Bearings
The University of Texas Center for Electromechanics (UT-CEM) in association with the Texas A&M Vibration Control Lab (TAMU-VCL) has developed an active magnetic bearing control system for use in a 5 MW, 25 MJ, 20,000 RPM flywheel alternator developed under the Combat Hybrid Power Systems (CHPS) program. The inside-out topology of this flywheel (i.e., the 650 lb (294 kg) flywheel rotor is positioned outside the stator) was dictated by the extreme power density and energy density requirements, and presented unique control challenges seldom encountered in conventional magnetic bearing applications. These challenges resulted from a large number of flexible modes in the rotor and stator, requiring a high-order flexible dynamic model and extensive rotordynamic analysis. A simulation-based design effort was implemented to accomplish the primary control objective: to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. Additionally, this design effort provided critical specifications for CHPS flywheel design and component selection. Details of the CHPS magnetic bearing design, prototyping, and testing are presented in a companion paper “Inside-Out Configuration Active Magnetic Bearing Actuators”.Center for Electromechanic