A hybrid drivetrain comprising a 16 kW polymer electrolyte membrane fuel cell system, ultracapacitor modules and a lead-acid battery was constructed and experimentally tested in a real counterweight forklift application. A scaled-down version of the hybrid system was assembled and tested in a controlled laboratory environment using a controllable resistive load. The control loops were operating in an in-house developed embedded system. The software is designed for building generic control applications, and the source code has been released as open source and made available on the internet. The hybrid drivetrain supplied the required 50 kW peak power in a typical forklift work cycle consisting of both loaded and unloaded driving, and lifting of a 2.4 tonne load. Load variations seen by the fuel cell were a fraction of the total current drawn by the forklift, with the average fuel cell power being 55% of nominal rating. A simple fuel cell hybrid model was also developed to further study the effects of energy storage dimensioning. Simulation results indicate that while a battery alone significantly reduces the load variations of the fuel cell, an ultracapacitor reduces them even further. Furthermore, a relatively small ultracapacitor is enough to achieve most of the potential benefit.
Keränen, T., Karimäki, H., Viitakangas, J., Vallet, J., Ihonen, J., Hyötylä, P., Uusalo, H., & Tingelöf, T. (2011). Development of integrated fuel cell hybrid power source for electric forklift. Journal of Power Sources, 196(21), 9058-9068. https://doi.org/10.1016/j.jpowsour.2011.01.025