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Simulation of a Flywheel Energy-Storage System

Wheel acceleration, wheel deceleration, and switching voltage transients are represented.

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.

Topics:
Attitude control Avionics CAD, CAM and CAE Computer simulation Engine components Engine mechanical components Engines Flight control systems Flywheels Information Technology Off-board energy sources Powertrains Simulation and modeling Solar energy Spacecraft Transmissions Vehicles
This Brief includes a Technical Support Package (TSP).
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Simulation of a Flywheel Energy-Storage System

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

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    Defense Tech Briefs Magazine

    This article first appeared in the February, 2008 issue of Defense Tech Briefs Magazine (Vol. 2 No. 1).

    Read more articles from the archives here.

    Overview

    The document presents a comprehensive overview of the Flywheel Attitude Control, Energy Transmission, and Storage (FACETS) system, developed at the Air Force Research Laboratory's Space Vehicles Directorate in Kirtland AFB, NM. The FACETS system is designed to demonstrate integrated attitude control maneuvers and energy storage capabilities for spacecraft, particularly in the context of space radar applications.

    The power subsystem of FACETS consists of three advanced flywheel units connected in parallel to a 150V main bus, which is also linked to a solar array. This configuration allows the system to efficiently manage power distribution for various operational modes: charge, discharge, and standby. In charge mode, the flywheels are connected to the main bus through a buck converter, which regulates the DC voltage of the inverter and controls the spin-up rate of the flywheels. During discharge mode, the flywheels supply power to the spacecraft via a rectifier and boost converter. Standby mode occurs when sunlight is available, and the flywheels have reached their maximum spin speeds, allowing for energy storage without active power generation.

    The document details the modeling of the FACETS power system using Matlab Simulink, employing state space averaged models based on Cuk’s methods for averaged power converters. This modeling approach enables the simulation of the system's performance over an orbital profile derived from a notional space radar application. The results of the simulations are compared to previous power subsystem simulations conducted by the FACETS program, validating the effectiveness of the model.

    The authors, Claus R. Danielson, Nicolas W. Frank, and Brian Wilson, emphasize the importance of flywheel energy storage systems in modern spacecraft design, particularly for applications requiring rapid power delivery and efficient energy management. The FACETS system serves as a critical tool for advancing the understanding of energy storage technologies and their integration into spacecraft power systems.

    Overall, the document highlights the innovative use of flywheel technology in aerospace applications, showcasing its potential to enhance the performance and reliability of spacecraft power systems while supporting advanced mission profiles.

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