J. H. Beno

Flywheel batteries come around again

Todays flywheel batteries, embody technological advances, and they are serious contenders for a variety of important energy-storage applications. They are, for example, competitive with chemical batteries in applications like transportation or improving power quality, which involve many charge-discharge cycles and little in the way of long-term storage. Progress in power electronics, particularly in high-power insulated-gate bipolar transistors (IGBTs) and field-effect transistors (FETs), underlies higher-power flywheel operation. While the stored energy is determined by the speed, mass, and geometry of the wheel, the limits on input and output power are in general set by the power electronics. With these higher power devices, fewer individual components are needed, so the power electronics package can be comparable in size to the flywheel plus motor-generator combination. This paper describes the main features of flywheel energy storage systems and space, hybrid electric vehicle, and combat vehicle applications.

Electric ship power system integration analyses through modeling and simulation

The Center for Electromechanics (CEM) at the University of Texas is engaged in the development of a comprehensive power system model in order to address several challenging issues facing the development of a viable and effective integrated power system architecture for future naval platforms. The power system under consideration reflects the notional DD power system architecture and is developed in the Matlab/Simulink environment. System components such as motors and generators are modeled using parameters based on actual machine design and analysis work performed at CEM. Simulation results of models including permanent-magnet propulsion motors and generators with simple reconfiguration scenarios simulating loss and recovery of power to propulsion and vital loads are presented.

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 characteristics.

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.

Current status of the Hobby-Eberly Telescope wide-field upgrade

The Hobby-Eberly Telescope (HET) is an innovative large telescope of 9.2 meter aperture, located in West Texas at the McDonald Observatory (MDO). The HET operates with a fixed segmented primary and has a tracker which moves the four-mirror corrector and prime focus instrument package to track the sidereal and non-sidereal motions of objects. A major upgrade of the HET is in progress that will increase the pupil size to 10 meters and the field of view to 22′ by replacing the corrector, tracker and prime focus instrument package. In addition to supporting the existing suite of instruments, this wide field upgrade will feed a revolutionary new integral field spectrograph called VIRUS, in support of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEXχ). This paper discusses the current status of this upgrade.

Directly-Coupled Gas Turbine Permanent Magnet Generator Sets for Prime Power Generation On Board Electric Ships

Prime power generation on board all-electric ships presents several options that affect fuel consumption, power density, operational effectiveness, and survivability. A study that aims at understanding the effects of some of these options has been conducted and results are reported in this paper. It is found that direct coupling of gas turbines to permanent magnet generators reduces system mass and volume significantly as compared to electric power generation systems installed on present-day navy ships. Furthermore, it is found that a significant benefit this topology brings is a reduction in gas turbine air duct volume if the compact gen-set units are relocated on or near the ships upper decks. In addition, a combinatory analysis revealed that the choice of the number of generating units and their respective power levels has a significant influence on overall efficiency.

Flywheel batteries for vehicles

Energy storage flywheels are useful in power conditioning applications, i.e. when there is a mismatch between the power generated and the power required by the load. Two examples of this mismatch are a temporal mismatch and a mismatch in magnitude. The use of a flywheel in a hybrid vehicle, for example, permits the engine to be designed to provide only the power needed to overcome steady-state losses and not have the inefficiencies that result when the engine must also provide power for maximum acceleration. While power management has provided the opportunities for flywheel batteries in vehicles, advances in technology have made the systems more practical. The key advance is the development of very high strength, long-life composites. These materials have significantly improved the energy density in the system over what could be achieved with a steel wheel by permitting much higher rotational velocities. So smaller, lighter wheels can store energy in the range from less than a kilowatt-hour to more than 100 kilowatt-hours. Other important advances have been in magnetic bearings that allow reliable high-speed operation and in power electronics to control the output power. Vehicular operation does produce new issues that were less significant in the more traditional stationary applications. One of the most obvious among these is torque management. In charging or discharging a flywheel, the rotational velocity is changed and a torque is produced. For example, systems intended for the International Space Station, where torque management is critical, the initial plan is to cancel torque by using two counter-rotating flywheels. Once confidence is gained in this mode of operation, energy will be distributed among various flywheels to produce the net torque needed for stable operation. For terrestrial vehicles, the flywheel is in a gimbled compliant mount with the axis of rotation orthogonal to the plane of vehicle motion. This orientation permits torque to be compensated by the magnetic bearings and the mount. Tests show that the mount and bearing system can accommodate the shock and vibrations, as well as traveling up or down grades, expected under on-road operation.

BEARING LOADS IN A VEHICULAR FLYWHEEL BATTERY

Radial and axial rotor support bearings are critical elements in flywheel batteries for vehicle applications. This paper discusses the quantification of bearing loads required for the development of optimal bearing designs, particularly magnetic bearings. The primary contributors to bearing loads are shown to be vehicle shock, vibration, maneuvering, and gyrodynamics. Emphasis is placed on transit bus applications. Available data for each is presented, including actual measurements made on buses, and a detailed analysis of gyrodynamics.

Design and development of a long-travel positioning actuator and tandem constant force actuator safety system for the Hobby Eberly Telescope wide-field upgrade

The Wide Field Upgrade presents a five-fold increase in mass for the Hobby-Eberly Telescopes* tracker system. The design of the Hobby-Eberly Telescope places the Prime Focus Instrument Package (PFIP) at a thirty-five degree angle from horizontal. The PFIP and its associated hardware have historically been positioned along this uphill axis (referred to as the telescopes Y-axis) by a single screw-type actuator. Several factors, including increased payload mass and design for minimal light obscuration, have led to the design of a new and novel configuration for the Y-axis screw-drive as part of the tracker system upgrade. Typical screw-drive designs in this load and travel class (approximately 50 kilonewtons traveling a distance of 4 meters) utilize a stationary screw with the payload translating with the moving nut component. The new configuration employs a stationary nut and translating roller screw affixed to the moving payload, resulting in a unique drive system design. Additionally, a second cable-actuated servo drive (adapted from a system currently in use on the Southern African Large Telescope) will operate in tandem with the screw-drive in order to significantly improve telescope safety through the presence of redundant load-bearing systems. Details of the mechanical design, analysis, and topology of each servo drive system are presented in this paper, along with discussion of the issues such a configuration presents in the areas of controls, operational and failure modes, and positioning accuracy. Findings and results from investigations of alternative telescope safety systems, including deformable crash barriers, are also included.

Electromechanical Active Suspension Demonstration for Off-Road Vehicles

The University of Texas Center for Electromechanics (UTCEM) has been developing active suspension technology for offroad and on-road vehicles since 1993. The UT-CEM approach employs fully controlled electromechanical (EM) actuators to control vehicle dynamics and passive springs to efficiently support vehicle static weight. The program has completed three phases (full scale proof-of-principle demonstration on a quartercar test rig; algorithm development on a four-corner test rig; and advanced EM linear actuator development) and is engaged in a full vehicle demonstration phase. Two full vehicle demonstrations are in progress: an off-road demonstration on a high mobility multiwheeled vehicle (HMMWV) and an on-road demonstration on a transit bus. HMMWV test results are indicating significant reductions in vehicle sprung mass accelerations with simultaneous increases in cross-country speed when compared to conventional passive suspension systems. Additionally, original projections of low power requirements for suspension actuators are being confirmed. The 3,400 kg (3.75 ton) vehicle being tested utilizes a 5 kW alternator to provide suspension power. Power conditioning circuits limit the continuous deliverable power to 4 kW, which corresponds to 1.2 kW/metric