Air friction losses in PM BLDC motor with external rotor operating as kinetic energy storage system

Moment of inertia of motor with external rotor is much higher than this moment for motor with internal rotor and identical power rating. This characteristic may be utilized for designing kinetic energy storage using electric motor. Problems occurring when brushless dc motor (PM BLDC) with external rotor is employed as kinetic energy storage are discussed in the paper. Design recommendations for reducing these problems are also given. The analysis is supported by results of laboratory tests run with motor manufactured to scale.