Design principles for a flywheel energy store for road vehicles

This paper introduces a flywheel energy storage device capable of enhancing the fuel economy of a hybrid-type road vehicle. A number of possible drive types is considered and the permanent magnet machine drive is shown to provide the best solution. Reasons for selecting a device using an axial-field configuration with single rotor and double stator sections are described. Electrical, magnetic and mechanical design data are presented for a full-scale prototype device with 240 kJ of usable energy storage and 25 kW of power transfer, operating at speeds up to 50000 revs per minute, with a 10% duty cycle.