Development of integrated fuel cell hybrid power source for electric forklift
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.Research highlights► We built a hybrid power source for a heavy electric counterweight forklift. ► We study hybrid drivetrain with real work cycle data to validate modelling tools. ► Embedded control system hardware and software are released under open source license.
Available from: Billy Wu
- "Nishizawa et al.  developed a FCebattery passive hybrid system for aircraft applications and showed that there was an increase in efficiency compared to equivalent systems using DC/DC converters and that the lower impedance response of the battery resulted in more mild transient loads for the FC. Keranen et al.  developed a FCesupercapacitorebattery triple hybrid and showed that benefits of passive hybridisation could be achieved with a relatively small supercapacitor pack and that system voltage should be near the maximum voltage of the supercapacitor pack due to small voltage variations. Within the academic literature, there have been no systems that have studied passive hybridisation between a FC and supercapacitor. "
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ABSTRACT: The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling.
Electrochemical Impedance Spectroscopy measurements indicated that the supercapacitor capacitance dropped with decreasing cell voltage and suggested that operation below 1.3 V is not recommended. Knee-frequency measurements suggested little benefit was gained in using passive systems with load cycles that have frequency components above 0.19 Hz. Analysis of system sizing suggested using the minimum number of supercapacitors to match the open circuit voltage of the fuel cell to maximise load buffering.
Available from: Mykhaylo V LOTOTSKYY
- "Several attempts were undertaken to address the specified problem, mainly, by means of system modelling      . At the same time, quantitative information about the influence of introduction of a quite low-power fuel cell on the performance of battery electric vehicles is lacking and would be useful for the further modelling and optimisation activities. "
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ABSTRACT: A light electric vehicle (golf cart, 5 kW nominal motor power) was integrated with a commercial 1.2 kW PEM fuel cell system, and fuelled by compressed hydrogen (two com-posite cylinders, 6.8 L/300 bar each). Comparative driving tests in the battery and hybrid (battery þ fuel cell) powering modes were performed. The introduction of the fuel cell was shown to result in extending the driving range by 63e110%, when the amount of the stored H 2 fuel varied within 55e100% of the maximum capacity. The operation in the hybrid mode resulted in more stable driving performances, as well as in the increase of the total energy both withdrawn by the vehicle and returned to the vehicle battery during the driving. Statistical analysis of the power patterns taken during the driving in the battery and hybrid-powering modes showed that the latter provided stable operation in a wider power range, including higher frequency and higher average values of the peak power.
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ABSTRACT: The concept of passive hybrid, i.e. the direct electrical coupling between a fuel cell system and a battery without using a power converter, is presented as a feasible solution for powertrain applications. As there are no DC/DC converters, the passive hybrid is a cheap and simple solution and the power losses in the electronic hardware are eliminated. In such a powertrain topology where the two devices always have the same voltage, the active power sharing between the two energy sources can not be done in the conventional way. As an alternative, control of the fuel cell power by adjusting its operating pressure is elaborated. Only pure H2/O2 fuel cell systems are considered in this approach. Simulation and hardware in the loop (HIL) results for the powertrain show that this hybrid power source is able to satisfy the power demand of an electric vehicle while sustaining the battery state of charge.Highlights► Fuel cell hybrid vehicles are under consideration. ► We consider the direct electrical coupling of a fuel cell and a battery. ► The fuel cell power is actively controlled by adjusting its operating pressure. ► The power demand of a vehicle is fulfilled while sustaining the battery SOC. ► Without DC/DC converter, the hybrid powertrain becomes simpler and cheaper.
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