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NASA NTRS2002

New Approach to Ultrasonic Spectroscopy Applied to Flywheel Rotors

Flywheel energy storage devices comprising multilayered composite rotor systems are being studied extensively for use in the International Space Station. A flywheel system includes the components necessary to store and discharge energy in a rotating mass. The rotor is the complete rotating assembly portion of the flywheel, which is composed primarily of a metallic hub and a composite rim. The rim may contain several concentric composite rings. This article summarizes current ultrasonic spectroscopy research of such composite rings and rims and a flat coupon, which was manufactured to mimic the manufacturing of the rings. Ultrasonic spectroscopy is a nondestructive evaluation (NDE) method for material characterization and defect detection. In the past, a wide bandwidth frequency spectrum created from a narrow ultrasonic signal was analyzed for amplitude and frequency changes. Tucker developed and patented a new approach to ultrasonic spectroscopy. The ultrasonic system employs a continuous swept-sine waveform and performs a fast Fourier transform on the frequency spectrum to create the spectrum resonance spacing domain, or fundamental resonant frequency. Ultrasonic responses from composite flywheel components were analyzed at Glenn to assess this NDE technique for the quality assurance of flywheel applications.

Harmon, Laura M.↗

NASA NTRS2005

G2 Flywheel Module Operated at 41,000 rpm

NASA Glenn Research Center s Flywheel Development Team designed, built, and successfully operated the new G2 flywheel to 41,000 rpm on September 2, 2004. This work was supported by the Aerospace Flywheel Technology Program--a NASA Office of Aerospace Technology ETC Program funded by the Energetics Project. The work was performed by a team of civil servants, contractors, and grantees managed by Glenn s Electrical Systems Development Branch, Structural Mechanics and Dynamics Branch, and Space Power & Propulsion Test Engineering Branch. The G2 flywheel was designed to be a low-cost modular testbed for flywheel system integration and component demonstrations.

Ralph H Jansen↗

NASA NTRS2005

Single Axis Flywheel IPACS @1300W, 0.8 N-m

NASA Glenn Research Center is developing flywheels for space systems. A single axis laboratory version of an integrated power and attitude control (IPACs) system has been experimentally demonstrated. This is a significant step on the road to a flight qualified three axes IPACS system. The presentation outlines the flywheel development process at NASA GRC, the experimental hardware and approach, the IPACS control algorithm that was formulated and the results of the test program and then proposes a direction for future work. GRC has made progress on flywheel module design in terms of specific energy density and capability through a design and test program resulting in three flywheel module designs. Two of the flywheels are used in the 1D-IPACS experiment with loads and power sources to simulate a satellite power system. The system response is measured in three power modes: charge, discharge, and charge reduction while simultaneously producing a net output torque which could be used for attitude control. Finally, recommendations are made for steps that should be taken to evolve from this laboratory demonstration to a flight like system.

Jansen, Ralph↗

NASA NTRS1979

Safety flywheel

An inertial energy storage device is disclosed which uses flywheel made of flexible material such as a twisted rope ring. A small number of the strands of the rope ring have a tensile strength that is lower than that of most of the other strands so that should any of these strands fail, they will begin to whiplash allowing such a failure to be detected and braked before a castastrophic failure occurs. This accomplished by the inclusion of glass tubes located around the periphery of the flywheel. The tubes are in communication with a braking fluid reservoir. The flywheel and glass tubes are enclosed within a vacuum-tight housing. The whiplashing of a broken strand breaks one or more glass tubes. This causes the housing to be flooded with the braking fluid thereby braking the rotation of the flywheel.

Schneider, R. T.↗

NASA NTRS1984

A summary of the 1983 Integrated Flywheel Technology Workshop

The use of flywheels to perform the functions of attitude control and/or energy storage on a variety of space missions was studied. Integrated Flywheel Technology was discussed. The four primary objectives are: (1) determine the potential of flywheels for energy storage system applications and for combined energy storage and attitude control concepts; (2) assess the state of the art (SOA) in integrated flywheel technology through a review of government sponsored programs; (3) identify those technology areas which are in critical need of development to meet projected space mission requirements; (4) scope a program for the coordinated development of the required technology.

Keckler, C. R.↗

NASA NTRS1984

Merits of flywheels for spacecraft energy storage

Flywheel energy storage systems which have a very good potential for use in spacecraft are discussed. This system can be superior to alkaline secondary batteries and regenerable fuel cells in most of the areas that are important in spacecraft applications. Of special importance, relative to batteries, are lighter weight, longer cycle and operating life, and high efficiency which minimizes solar array size and the amount of orbital makeup fuel required. Flywheel systems have a long shelf life, give a precise state of charge indication, have modest thermal control needs, are capable of multiple discharges per orbit, have simple ground handling needs, and have characteristics which would be useful for military applications. The major disadvantages of flywheel energy storage systems are that: power is not available during the launch phase without special provisions; and in flight failure of units may force shutdown of good counter rotating units, amplifying the effects of failure and limiting power distribution system options; no inherent emergency power capability unless specifically designed for, and a high level of complexity compared with batteries. The potential advantages of the flywheel energy storage system far outweigh the disadvantages.

Gross, S.↗

NASA NTRS1984

Generic composite flywheel designs

Fiber reinforced composites belong to a new class of materials and allow great flexibility in flywheel design. The most efficient flywheel may no longer have the classic Stodola taper and indeed, may not even be round. Some of the flywheel designs that have been developed in the past are discussed. Although choice of material, mounts and service requirements often dictate the final design choice for a particular application, the composite flywheels in this paper are classified within a geometric framework, a simple stress analysis of a circular disk is carried out.

Steele, R. S.↗

NASA NTRS1984

Summary results of the DOE flywheel development effort

The technology and applications evaluation task focuses on defining performance and cost requirements for flywheels in the various areas of application. To date the DOE program has focused on automotive applications. The composite materials effort entails the testing of new commercial composites to determine their engineering properties. The rotor and containment development work uses data from these program elements to design and fabricate flywheels. The flywheels are then tested at the Oak Ridge Flywheel Evaluation Laboratory and their performance is evaluated to indicate possible areas for improvement. Once a rotor has been fully developed it is transferred to the private sector.

Olszewski, M.↗

NASA NTRS1987

Bidirectional control system for energy flow in solar powered flywheel

An energy storage system for a spacecraft is provided which employs a solar powered flywheel arrangement including a motor/generator which, in different operating modes, drives the flywheel and is driven thereby. A control circuit, including a threshold comparator, senses the output of a solar energy converter, and when a threshold voltage is exceeded thereby indicating the availability of solar power for the spacecraft loads, activates a speed control loop including the motor/generator so as to accelerate the flywheel to a constant speed and thereby store mechanical energy, while also supplying energy from the solar converter to the loads. Under circumstances where solar energy is not available and thus the threshold voltage is not exceeded, the control circuit deactivates the speed control loop and activates a voltage control loop that provides for operation of the motor as a generator so that mechanical energy from the flywheel is converted into electrical energy for supply to the spacecraft loads.

Nola, Frank J.↗

NASA NTRS1988

System characterization of a magnetically suspended flywheel

The purpose of flywheel energy storage is to provide a means to save energy during times when the satellite is in sunlight, and then return the energy during the time when the satellite is in darkness. Typically, an energy storage device operates cyclically, where for satellites in Low Earth Orbit (LEO) the typical period is 60 minutes of sunlight followed by 30 minutes of darkness. If a lifetime of 17 years is required the energy storage system must be capable of sustaining approximately 100,000 cycles. The recent developments at the University of Maryland and how these progressions apply to a 500 Watt-hour magnetically suspended flywheel stack energy storage system are covered. The work includes hardware testing results from a stack flywheel energy storage system, improvements in the area of non-contacting displacement transducers, and performance enhancements of magnetic bearings. The experimental results show that a stack flywheel energy storage system is a feasible technology.

Kirk, James A.↗

NASA NTRS1992

Development of a differentially balanced magnetic bearing and control system for use with a flywheel energy storage system

The purpose of a magnetically suspended flywheel energy storage system for electric utility load leveling is to provide a means to store energy during times when energy is inexpensive to produce and then return it to the customer during times of peak power demand when generated energy is most expensive. The design of a 20 kWh flywheel energy storage system for electric utility load leveling applications involves the successful integration of a number of advanced technologies so as to minimize the size and cost of the system without affecting its efficiency and reliability. The flywheel energy storage system uses a carbon epoxy flywheel, two specially designed low loss magnetic bearings, a high efficiency motor generator, and a 60 cycle AC power converter all integrated through a microprocessor controller. The basic design is discussed of each of the components that is used in the energy storage design.

Higgins, Mark A.↗

NASA NTRS1999

International Space Station Attitude Control and Energy Storage Experiment: Effects of Flywheel Torque

The Attitude Control and Energy Storage Experiment is currently under development for the International Space Station; two counter-rotating flywheels will be levitated with magnetic bearings and placed in vacuum housings. The primary objective of the experiment is to store and discharge energy, in combination with existing batteries, into the electrical power system. The secondary objective is to use the flywheels to exert torque on the Station; a simple torque profile has been designed so that the Station's Control Moment Gyroscopes will be assisted in maintaining torque equilibrium attitude. Two energy storage contingencies could result in the inadvertent application of torque by the flywheels to the Station: an emergency shutdown of one flywheel rotor while the other remains spinning, and energy storage with only one rotor instead of the counterrotating pair. Analysis of these two contingencies shows that attitude control and the microgravity environment will not be adversely affected.

Roithmayr, Carlos M.↗

NASA NTRS2000

Simulation of a Flywheel Electrical System for Aerospace Applications

A Flywheel Energy Storage Demonstration Project was initiated at the NASA Glenn Research Center as a possible replacement for the battery energy storage system on the International Space Station (ISS). While the hardware fabrication work was being performed at a university and contractor's facility, the related simulation activity was begun at Glenn. At the top level, Glenn researchers simulated the operation of the ISS primary electrical system (as described in another paper) with the Flywheel Energy Storage Unit (FESU) replacing one Battery Charge and Discharge Unit (BCDU). The FESU consists of a Permanent Magnet Synchronous Motor/Generator (PMSM), which is connected to the flywheel; the power electronics that connects the PMSM to the ISS direct-current bus; and the associated controller. The PMSM model is still under development, but this paper describes the rest of the FESU model-the simulation of the converter and the associated control system that regulates energy transfer to and from the flywheel.

Truong, Long V.↗

NASA NTRS2001

International Space Station Bus Regulation With NASA Glenn Research Center Flywheel Energy Storage System Development Unit

An experimental flywheel energy storage system is described. This system is being used to develop a flywheel based replacement for the batteries on the International Space Station (ISS). Motor control algorithms which allow the flywheel to interface with a simplified model of the ISS power bus, and function similarly to the existing ISS battery system, are described. Results of controller experimental verification on a 300 W-hr flywheel are presented.

Kascak, Peter E.↗

NASA NTRS2003

Integrated Power and Attitude Control for a Spacecraft with Flywheels and Control Moment Gyroscopes

A law is designed for simultaneous control of the orientation of an Earth-pointing spacecraft, the energy stored by counter-rotating flywheels, and the angular momentum of the flywheels and control moment gyroscopes used together as all integrated set of actuators for attitude control. General. nonlinear equations of motion are presented in vector-dyadic form, and used to obtain approximate expressions which are then linearized in preparation for design of control laws that include feedback of flywheel kinetic energy error as it means of compensating for damping exerted by rotor bearings. Two flywheel 'steering laws' are developed such that torque commanded by all attitude control law is achieved while energy is stored or discharged at the required rate. Using the International Space Station as an example, numerical simulations are performed to demonstrate control about a torque equilibrium attitude and illustrate the benefits of kinetic energy error feedback.

Roithmayr, Carlos M.↗

NASA NTRS2004

Inverter Output Filter Effect on PWM Motor Drives of a Flywheel Energy Storage System

NASA Glenn Research Center (GRC) has been involved in the research and development of high speed flywheel systems for small satellite energy storage and attitude control applications. One research and development area has been the minimization of the switching noise produced by the pulsed width modulated (PWM) inverter that drives the flywheel permanent magnet motor/generator (PM M/G). This noise can interfere with the flywheel M/G hardware and the system avionics hampering the full speed performance of the flywheel system. One way to attenuate the inverter switching noise is by placing an AC filter at the three phase output terminals of the inverter with the filter neutral point connected to the DC link (DC bus) midpoint capacitors. The main benefit of using an AC filter in this fashion is the significant reduction of the inverter s high dv/dt switching and its harmonics components. Additionally, common mode (CM) and differential mode (DM) voltages caused by the inverter s high dv/dt switching are also reduced. Several topologies of AC filters have been implemented and compared. One AC filter topology consists of a two-stage R-L-C low pass filter. The other topology consists of the same two-stage R-L-C low pass filter with a series connected trap filter (an inductor and capacitor connected in parallel). This paper presents the analysis, design and experimental results of these AC filter topologies and the comparison between the no filter case and conventional AC filter.

Santiago, Walter↗

NASA NTRS1997

NASA Flywheel Program

NASA Lewis Research Center's Electrical Systems Development Branch is leading a program to develop space flywheel energy storage with integrated attitude control systems. The objective of this effort is to develop a flywheel system that will reduce spacecraft infrastructure weight and improve power system efficiency. Additional potential benefits of these systems are their increased life and improved system operation. These potential advantages are due to a flywheel system's very large number of charge/recharge cycles and their known state of charge. Our multifaceted program consists of efforts to develop flywheels, and their components, as well as the facilities to test them.

Kaufman, Bradford A.↗

NASA NTRS2001

Flywheel Energy Storage Technology Being Developed

A flywheel energy storage system was spun to 60,000 rpm while levitated on magnetic bearings. This system is being developed as an energy-efficient replacement for chemical battery systems. Used in groups, the flywheels can have two functions providing attitude control for a spacecraft in orbit as well as providing energy storage. The first application for which the NASA Glenn Research Center is developing the flywheel is the International Space Station, where a two-flywheel system will replace one of the nickel-hydrogen battery strings in the space station's power system. The 60,000-rpm development rotor is about one-eighth the size that will be needed for the space station (0.395 versus 3.07 kWhr).

Wolff, Frederick J.↗