A New Energy Management System of Directly-Driven Electric Vehicle with Electronic Gearshift and Regenerative Braking

This paper proposes a novel energy management system with electronic gearshift and regenerative braking to improve the gross efficiency and driving range of an electric vehicle. This electric motorcycle is driven directly by a wheel motor, which is a custom-designed disk-type axial-flux dc brushless motor. Its stator windings are grouped into four phases and are connected in parallel or serially for high or low speed ranges. The integration of windings, batteries, ultracapacitors and the core controller constitutes the energy management system, which features a natural and smooth shifting of gears and regenerative braking electronically. The control and energy management are coded in a field programmable gate array, which also functions for the calculation and display of the state of charge of batteries. The gross efficiency of this electric vehicle is improved in the driving range by 20% with respect to that without regenerative braking scheme according to the ECE47 standard of performance test. The motor-to-wheel efficiency also was above 70% at 30 km/hr with low speed gear and at 50 km/hr with high speed gear.