Flywheels Upgraded for Systems Research

With the advent of high-strength composite materials and microelectronics, flywheels are becoming attractive as a means of storing electrical energy. In addition to the high energy density that flywheels provide, other advantages over conventional electrochemical batteries include long life, high reliability, high efficiency, greater operational flexibility, and higher depths of discharge. High pulse energy is another capability that flywheels can provide. These attributes are favorable for satellites as well as terrestrial energy storage applications. In addition to energy storage for satellites, the several flywheels operating concurrently can provide attitude control, thus combine two functions into one system. This translates into significant weight savings. The NASA Glenn Research Center is involved in the development of this technology for space and terrestrial applications. Glenn is well suited for this research because of its world-class expertise in power electronics design, rotor dynamics, composite material research, magnetic bearings, and motor design and control. Several Glenn organizations are working together on this program. The Structural Mechanics and Dynamics Branch is providing magnetic bearing, controls, and mechanical engineering skills. It is working with the Electrical Systems Development Branch, which has expertise in motors and generators, controls, and avionics systems. Facility support is being provided by the Space Electronic Test Engineering Branch, and the program is being managed by the Space Flight Project Branch. NASA is funding an Aerospace Flywheel Technology Development Program to design, fabricate, and test the Attitude Control/Energy Storage Experiment (ACESE). Two flywheels will be integrated onto a single power bus and run simultaneously to demonstrate a combined energy storage and 1-degree-of-freedom momentum control system. An algorithm that independently regulates direct-current bus voltage and net torque output will be experimentally demonstrated

Integrated Power and Attitude Control System Demonstrated With Flywheels G2 and D1

On September 14, 2004, NASA Glenn Research Center's Flywheel Development Team experimentally demonstrated a full-power, high-speed, two-flywheel system, simultaneously regulating a power bus and providing a commanded output torque. Operation- and power-mode transitions were demonstrated up to 2000 W in charge and 1100 W in discharge, while the output torque was simultaneously regulated between plus or minus 0.8 N-m. The G2 and D1 flywheels--magnetically levitated carbon-fiber wheels with permanent magnet motors--were used for the experiment. The units were mounted on an air bearing table in Glenn's High Energy Flywheel Facility. The operational speed range for these tests was between 20,000 and 60,000 rpm. The bus voltage was regulated at 125 V during charge and discharge, and charge-discharge and discharge-charge transitions were demonstrated by changing the amount of power that the power supply provided between 300 and 0 W. In a satellite system, this would be the equivalent of changing the amount of energy that the solar array provides to the spacecraft. In addition to regulating the bus voltage, we simultaneously controlled the net torque produced by the two flywheel modules. Both modules were mounted on an air table that was restrained by a load cell. The load cell measured the force on the table, and the torque produced by the two flywheels on the table could be calculated from that measurement. This method was used to measure the torque produced by the modules, yielding net torques from -0.8 to 0.8 N-m. This was the first Glenn demonstration of the Integrated Power and Attitude Control System (IPACS) at high power levels and speeds

Sizing Power Components of an Electrically Driven Tail Cone Thruster and a Range Extender

The aeronautics industry has been challenged on many fronts to increase efficiency, reduce emissions, and decrease dependency on carbon-based fuels. This paper provides an overview of the turboelectric and hybrid electric technologies being developed under NASA's Advanced Air Transportation Technology (AATT) Project and discusses how these technologies can impact vehicle design. The discussion includes an overview of key hybrid electric studies and technology investments, the approach to making informed investment decisions based on key performance parameters and mission studies, and the power system architectures for two candidate aircraft. Finally, the power components for a single-aisle turboelectric aircraft with an electrically driven tail cone thruster and for a hybrid-electric nine-passenger aircraft with a range extender are parametrically sized, and the sensitivity of these components to key parameters is presented

Control system for bearingless motor-generator

A control system for an electromagnetic rotary drive for bearingless motor-generators comprises a winding configuration comprising a plurality of individual pole pairs through which phase current flows, each phase current producing both a lateral force and a torque. A motor-generator comprises a stator, a rotor supported for movement relative to the stator, and a control system. The motor-generator comprises a winding configuration supported by the stator. The winding configuration comprises at least three pole pairs through which phase current flows resulting in three three-phase systems. Each phase system has a first rotor reference frame axis current that produces a levitating force with no average torque and a second rotor reference frame axis current that produces torque

Control System for Bearingless Motor-generator

A control system for an electromagnetic rotary drive for bearingless motor-generators comprises a winding configuration comprising a plurality of individual pole pairs through which phase current flows, each phase current producing both a lateral force and a torque. A motor-generator comprises a stator, a rotor supported for movement relative to the stator, and a control system. The motor-generator comprises a winding configuration supported by the stator. The winding configuration comprises at least three pole pairs through which phase current flows resulting in three three-phase systems. Each phase system has a first rotor reference frame axis current that produces a levitating force with no average torque and a second rotor reference frame axis current that produces torque

Partially Turboelectric Aircraft Drive Key Performance Parameters

The purpose of this paper is to propose electric drive specific power, electric drive efficiency, and electrical propulsion fraction as the key performance parameters for a partially turboelectric aircraft power system and to investigate their impact on the overall aircraft performance. Breguet range equations for a base conventional turbofan aircraft and a partially turboelectric aircraft are found. The benefits and costs that may result from the partially turboelectric system are enumerated. A break even analysis is conducted to find the minimum allowable electric drive specific power and efficiency, for a given electrical propulsion fraction, that can preserve the range, fuel weight, operating empty weight, and payload weight of the conventional aircraft. Current and future power system performance is compared to the required performance to determine the potential benefit

Experimental Performance Evaluation of a High Speed Permanent Magnet Synchronous Motor and Drive for a Flywheel Application at Different Frequencies

This paper presents the results of an experimental performance characterization study of a high speed, permanent magnet motor/generator (M/G) and drive applied to a flywheel module. Unlike the conventional electric machine the flywheel M/G is not a separated unit; its stator and rotor are integrated into a flywheel assembly. The M/G rotor is mounted on a flywheel rotor, which is magnetically levitated and sealed within a vacuum chamber during the operation. Thus, it is not possible to test the M/G using direct load measurements with a dynamometer and torque transducer. Accordingly, a new in-situ testing method had to be developed. The paper describes a new flywheel M/G and drive performance evaluation technique, which allows the estimation of the losses, efficiency and power quality of the flywheel high speed permanent magnet M/G, while working in vacuum, over wide frequency and torque ranges. This method does not require any hardware modification nor any special addition to the test rig. This new measurement technique is useful for high-speed applications, when applying an external load is technically difficult

High Specific Power Motors in LN2 and LH2

A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/cm2, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2

Overview of NASA Electrified Aircraft Propulsion Research for Large Subsonic Transports

NASA is investing in Electrified Aircraft Propulsion (EAP) research as part of the portfolio to improve the fuel efficiency, emissions, and noise levels in commercial transport aircraft. Turboelectric, partially turboelectric, and hybrid electric propulsion systems are the primary EAP configurations being evaluated for regional jet and larger aircraft. The goal is to show that one or more viable EAP concepts exist for narrow body aircraft and mature tall-pole technologies related to those concepts. A summary of the aircraft system studies, technology development, and facility development is provided. The leading concept for mid-term (2035) introduction of EAP for a single aisle aircraft is a tube and wing, partially turbo electric configuration (STARC-ABL), however other viable configurations exist. Investments are being made to raise the TRL level of light weight, high efficiency motors, generators, and electrical power distribution systems as well as to define the optimal turbine and boundary layer ingestion systems for a mid-term tube and wing configuration. An electric aircraft power system test facility (NEAT) is under construction at NASA Glenn and an electric aircraft control system test facility (HEIST) is under construction at NASA Armstrong. The correct building blocks are in place to have a viable, large plane EAP configuration tested by 2025 leading to entry into service in 2035 if the community chooses to pursue that goal

Counteracting Rotor Imbalance in a Bearingless Motor System with Feedforward Control

In standard motor applications, traditional mechanical bearings represent the most economical approach to rotor suspension. However, in certain high performance applications, rotor suspension without bearing contact is either required or highly beneficial. Such applications include very high speed, extreme environment, or limited maintenance access applications. This paper extends upon a novel bearingless motor concept, in which full five-axis levitation and rotation of the rotor is achieved using two motors with opposing conical air-gaps. By leaving the motors' pole-pairs unconnected, different d-axis flux in each pole-pair is created, generating a flux imbalance which creates lateral force. Note this is approach is different than that used in previous bearingless motors, which use separate windings for levitation and rotation. This paper will examine the use of feedforward control to counteract synchronous whirl caused by rotor imbalance. Experimental results will be presented showing the performance of a prototype bearingless system, which was sized for a high speed flywheel energy storage application, with and without feedforward control