A computational model has been developed to simulate the operation of a laboratory flywheel energy-storage system that is a subsystem of the Flywheel Attitude Control, Energy Transmission, and Storage (FACETS) system located at Kirtland Air Force Base in New Mexico. The FACETS, which includes three advanced flywheel energy-storage units and an apparatus denoted the Agile Multi- Purpose Satellite Simulator (AMPSS), is used to demonstrate conceptual spacecraft operations involving integral combinations of attitude-control maneuvers and energy-storage operations. The flywheel units include high-hoop-strength carbon composite rotors that turn on magnetic bearings. The flywheels have a maximum rated angular speed of 40,000 rpm, making it possible to store as much a 1 kW·hr of energy in each unit. An air bearing supports the entire AMPSS test article allowing three-axis rotation with minimal damping. In addition to the flywheel units, the system includes DC-to-DC power converters and a three-phase rectifier.

The FACETS power system operates in three modes: charge, discharge, and standby. The charge mode corresponds to the power mode of a notional spacecraft when the Sun is visible from the spacecraft and the power demand is less than the incoming solar power. In this mode, solar photovoltaic arrays that are parts of the notional spacecraft provide the power to spin up the flywheels and satisfy the housekeeping power demand of the spacecraft. The discharge mode takes place during eclipse or high power demand. In this mode, the flywheels provide power to the notional spacecraft and space radar systems. The standby mode corresponds to the notional spacecraft power mode in which sunlight is available but the flywheels have reached their maximum rated angular speed.

The computational model of the FACETS flywheel energy-storage system was constructed partly by use of permanent- magnet synchronous-machine and the universal-bridge blocks provided in the Matlab Simulink software package. High-fidelity electrical models of the DC-to-DC power converters and the three-phase rectifier were found to be too computationally intensive and, therefore, were replaced with state-space- averaged models.

A notional space radar application was selected for the FACETS mission profile. Space radar requires extremely large pulse power and, therefore, is an ideal application for flywheel energy storage. The model was demonstrated over an orbital profile derived from the notional space radar application. The model was verified by comparing its output with results of prior power-subsystem simulations performed in the FACETS program. Realistic phenomena represented by the results of the simulations included increase of flywheel speed during charge, steady flywheel speed during standby, decreasing flywheel speed during discharge, and voltage transients during transitions between charge and discharge.

This work was done by Claus R. Danielson of Sequoia Technologies, Nicolas W. Frank of Texas Agricultural and Mechanical University, and Brian Wilson of Draper Laboratories for the Air Force Research Laboratory.

This Brief includes a Technical Support Package (TSP).
Simulation of a Flywheel Energy-Storage System

(reference AFRL-0062) is currently available for download from the TSP library.

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