An Assessment of Flywheel Energy Storage in Electric Vehicles

The analysis and design of a hybrid drive for a 7.5 tonne urban delivery van is described. The drive consists of a flywheel to supply the power for vehicle acceleration and a battery pack and compound-wound d.c. motor to supply the steady-state power requirements. 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 are compared. It is concluded that rolling friction drives offer the best solution for vehicle applications. Results of a digital simulation are presented comparing the hybrid drive with an equivalent electric drive when the vehicle follows a standard duty cycle. The simulation is used to study the effect of varying the capacity of the flywheel and the benefits of regenerative braking are evaluated. It is shown that the hybrid drive gives a significant increase in vehicle range.