An Assessment of Flywheel Energy Storage in Electric Vehicles

The analysis and design of a hybrid drive for a 7.5-tonne (8.4 ton) urban delivery van are described. The drive consists of a flywheel for vehicle acceleration, and a battery pack and compound-wound direct current motor for steady-state power. The motor output is automatically regulated and the continuously variable transmission (CVT) is controlled to match the flywheel to the vehicle demand. Various types of CVT are considered, and their relative merits compared. It is concluded that rolling friction drives offer the best solution for vehicle applications. Digital simulation results are presented comparing the hybrid with an equivalent electric drive for a standard vehicle duty cycle. The effect of varying the flywheel capacity and regenerative braking benefits are examined. It is shown that the hybrid drive offers a significant increase in vehicle range.