Testing of Magnetic Bearings for Flywheel Energy Storage in Simulated Space Conditions

Abstract

†Energy storage is requir ed for all spacecraft that orbit the Earth and are eclipsed by the Earth’s shadow. Magnetic bearings are vital to the operation of flywheel energy storage systems because they operate without lubricants and reduce the drag losses to tolerable levels, allow ing flywheels to compete with batteries in terms of energy storage density. In addition, combining energy storage and attitude control into a single multi -wheel system realizes further mass savings. Sensor and control algorithm improvements are also vital to the operation of flywheel energy storage systems because of issues of balance, stress, and linkage with the motor/generator. Current commercial magnetic bearing applications have been for relatively low spin speed applications or where the ratio of mom ents of inertia were small (long, thin shafts). To increase energy storage density, it is necessary to utilize high strength composite wheels (with moment of inertia ratios of 1 or greater) rotating at high speed. High ratio of moment of inertia (short thi ck wheels) and high speed of rotation required with composite rotors compound the difficulty of control of the magnetic bearings. Previous work on this project led to the development of a magnetic bearing control algorithm demonstrated at 60,000 rpm and ro bust fault tolerant magnetic bearings and control systems for obtaining stable, low noise control of aerospace flywheels to greater than 60,000 rpm with low parasitic losses (minimal drag torque losses and power consumption by the feedback components). Thi s paper reports on efforts to provide early, inexpensive demonstrations of the magnetic bearing and control algorithms by testing a magnetically levitated flywheel in a simulated space environment. The experiment on the C -9 microgravity aircraft is to test the ability of a magnetic bearing to levitate and control a spinning shaft in microgravity, both under static conditions (constant shaft velocity) and during the momentum change of shaft acceleration and deceleration (energy storage and extraction). To si mulate space vacuum, the flywheel/magnetic bearing assembly is installed into a large vacuum chamber that the Center for Space Power has built and previously flight qualified on the KC -135.