Optimization and evaluation of an electro-mechanical battery/chemical battery series hybrid electric drivetrain for vehicular applications.

Abstract

This thesis presents the results of an optimization study of preliminary design objectives for a hybrid electric vehicle. The energy source is a lead-acid battery pack which is load levelled using an electro-mechanical battery. A control strategy or power split between the battery pack and electro-mechanical battery was devised such that a constant continuous low power output from the battery pack would result. The optimized hybrid electric drivetrain parameters, to maximize range, were: battery pack size = 620 kg, flywheel size = 0.58 kW$\cdot$h maximum energy storage capability, flywheel motor size = 30 kW rated continuous power output, drive motor size = 62 kW rated continuous power output, amount of energy initially stored in the flywheel = 0.50 kW$\cdot$h. The mini-van equipped with this optimized hybrid electric drivetrain would have a curb weight of 2070 kg and a payload capacity of 600 kg. In order to complete the Federal Urban Drive Schedule, the battery power output would be constant and set at 7.72 kW except during regenerative braking when the battery would be shut-off. Power peaks of up to 52 kW would be provided by the electro-mechanical battery with the flywheel speed remaining between 20 000 rpm and 40 000 rpm throughout the drive schedule. Total energy losses in the electro-mechanical battery incurred throughout the drive schedule result in a turnaround efficiency of 77.7%. The total amount of energy required from the battery pack in order for the vehicle to complete the 12 km long drive schedule is 2.31 kW$\cdot$h. The hybrid vehicle can repeat the drive schedule and travel a distance of 68 km using 80% of the battery's rated capacity. Thus, with a total mass of 858 kg, the hybrid drivetrain achieves and energy density of 13.6 W$\cdot$h/kg. Without the electro-mechanical battery to absorb the power peaks, energy density falls to 4.93 W$\cdot$h/kg for the electric drivetrain equipped with lead-acid batteries only. (Abstract shortened by UMI.)