Development of a Hybrid Energy Storage System for a Forklift Vehicle

This paper presents a prototype hybrid energy storage system with a Li-ion battery and a supercapacitor. Lithium-ion and supercapacitor sizing has been performed by testing the vehicle under different operating conditions (flat road take-off, flat road take-off with load, hill descent without load, hill ascent with load, and hill descent with load) to obtain the torque and power values required by the system. The longitudinal dynamics of the vehicle are analyzed, and the maximum power requirement is determined. Sizing equations have been used to find the ideal number of battery cells in addition to supercapacitors by considering the maximum operating currents. An interleaved buck/boost DC-DC converter is designed to charge and discharge the supercapacitor. Besides, the developed system is tested with different routes and speeds. Additionally, the results show that the hybrid system, especially the presence of a supercapacitor, leads to the reduction of the load on the battery and the increase in its lifetime.