Four New Technologies Demonstrated in Successful On-road Bus Test

The Center recently completed integration and Phase I testing of its high performance advanced flywheel system on the Advanced Technology Transit Bus (ATTB), meeting all program milestones and completing its DARPA, DOT, and Houston Metro Transit Bus Programs! After extensive laboratory testing, the flywheel system was integrated into the bus over the summer, debugged, tuned, and tested in September, demonstrating full hybrid electric vehicle operation with only the flywheel as energy storage. This final effort caps a major multi-year program with a long string of successes, many of which were “world firsts” at the time of completion. Some of the major successes, include:

• Development of high performance, composite rotor, flywheel system on fully active magnetic bearings, demonstrating 150 kW peak and 90 kW continuous power, and operation at speeds exceeding 40,000 RPM.

• Development of advanced motor generator controller, whose output can change from 0 to 90 kW in 5 ms with space vector, pulse-width-modulated control at 15 kHz switching frequency.

• Development of flywheel burst containment system, demonstrated to contain catastrophic burst failure in two full scale containment proof tests.

• Development of advanced composite rotor statistical design process, supported by advancements in hydroburst fatigue testing of composite flywheel rims.

• Full magnetic bearing control of a high-speed 130 lb rotor in a dual-axis gimbal system both in laboratory induced-shock environment and on operating transit bus.

• Full hybrid drive train operation of transit bus, with a flywheel integrated into energy management control scheme, recovering energy during vehicle braking and providing energy during acceleration. This system enabled the bus to double its acceleration rate with a simultaneous 28% reduction in power required from vehicle prime power unit.

• Simultaneous operation of all integrated advanced subsystems, including active suspension, the flywheel system, wheel motors, and hybrid electric drive train controller.

This major string of successes would not have been possible without the great team spirit and technical competence demonstrated by our industrial partners, especially CalNetix, PEI, and Test Devices (listed in alphabetical order). The program success was also enabled by the great leadership and support from the sponsors of flywheel storage research at CEM, especially, Center for Transportation and the Environment (CTE), DARPA, Houston Metro Transit, NASA-Glenn, State of Texas, and University of Texas (listed in alphabetical order).

For further information, please contact Dr. Joe Beno

Simulation-Based Power System Design

F. Zhang, R. Longoria, R. Thelen, and D. Wardell developed an effective approach to simulating the behavior of a hybrid electric train. The work was described in a paper titled, “A Simulation-Based Design Study for a Locomotive Electric Power System.” The paper was presented in the August Electrimacs 2002 conference held in Montreal, Canada. The authors developed a model and a simulation of the behavior for a conceptual locomotive power system consisting of a gas-turbine-driven synchronous alternator coupled to a circuit consisting of a rectifier, a dc link, and a variable frequency inverter. This system drives four traction motors and is integrated with a flywheel for energy storage. Such a hybrid power system meets demands for rapid acceleration, speed maintenance on grades, recovery of braking energy, and improved fuel efficiency. This work permits the simulation of the turbine, locomotive, and flywheel performance over real or hypothetical routes. The hybrid power system, including a high-speed generator and a flywheel that can provide 2 MW for three minutes, is being constructed at the Center.

For further information, please contact Dr. R. Longoria.

New Flywheel Design Presented

Richard Thompson, Joe Beno, and Tony Pac presented a description of a novel flywheel design at the 37th Intersociety Energy Conversion Engineering Conference, July 2002, in Washington, DC. Their presentation is titled, “Advanced Flywheel Technology for Space Applications.” The novel flywheel incorporates a composite arbor to reduce the system weight. The new design stores about 75% more energy per kilogram of flywheel mass than the current design, which uses a solid composite wheel. The primary technical challenge was to design, and subsequently construct, a composite arbor with the required mechanical properties. The successful design and construction were done using a new winding code developed at the Center for Electromechanics. This code predicts the as-wound mechanical properties of the final structure from any winding profile chosen. It can also be downloaded into the winding machine when a final winding approach has been selected, allowing rapid prototyping of filament-wound composite structures.