A HIGH-EFFICIENCY ELECTROMECHANICAL BATTERY

In our increasingly electrified society there is a growing need for ef ficient cost-effective means for storing electrical energy. The electr ic auto is a prime example. Storage systems for the electric utilities , and for wind or solar power, are other examples. While electrochemic al cells could in principle supply these needs, existing E-C batteries have well-known limitations. This article addresses an alternative-th e electromechanical battery (EMB). An EMB is a modular unit consisting of an evacuated housing containing a fiber-composite rotor. The rotor is supported by magnetic bearings and contains an integrally mounted permanent magnet array. Recent developments in high-strength fibers, i n permanent-magnet materials, and in solid-state power electronics ope n up new possibilities, allowing the design of small (1 kW-h) modular EMB's for full- or hybrid-electric vehicles, and larger size modules ( 25 kW-h), for a variety of stationary storage needs. The article addre sses design issues for EMBs with rotors made up of nested cylinders. I ssues addressed include: rotational stability, stress distributions, g enerator/motor power and efficiency, power conversion, and cost. An im portant conclusion; the use of EMB's in electric autos could result in a five-fold reduction (relative to the IC engine) in the primary ener gy input required for urban driving, with a concomitant major positive impact on our economy and on air pollution.