Practical Implementation of an Hybrid Electric-Fuel Cell Vehicle

Electric vehicles are becoming more popular in the consumer world, as the demand for high-performance vehicles continues along an upward trajectory. While the costs of fossil fuels and clean energy are on the rise, vehicles whose power sources operate together within an electric or hybrid framework continue to be in high demand. A major advance in hybrid vehicle research has focused on fuel cell technology. This technology has improved significantly over the past few years, with a major decrease in the cost, the volume and the weight of individual cells. In fact, medium power fuel cells are now available in medium-high efficiency. In order to develop a “competitive product…” “[h]igh performance fuel-cell power modules, batteries and the necessary power electronics …are required” and must be developed for greatest efficiency. Dominguez et al. introduce a hybrid vehicle, built from the commercial vehicle GEM eL by Global Electric Motorcars, where the battery stack of the commercial car is supported by a 4 kW fuel cell. The “fuel cell charges the batteries when they have low charge but it provides…power directly to the dc motor drive when it is required by the user.” Within the proposed hybrid system, Dominguez et al. divide the description of their system into the following subsections: the fuel cell device and the hydrogen storage system, the dc/dc power converter and the auxiliary converters, and the control and monitoring system. These three categories serve as the basis for analysis of the authors’ proposed hybrid vehicle. The proposed model has been “experimentally tested in the facilities of the National Institute of Aerospace Technology in Huelva, Spain, where two separate vehicle acceleration scenarios were tested.” In both of these scenarios, the authors observed that the fuel cell provides power whether or not the vehicle is in motion. The advantage to this system is that the vehicle range can be extended since the fuel cell module charges the batteries using hydrogen as fuel. The authors determine that after an analysis of their proposed hybrid vehicle system, their data demonstrate a “high robustness and reliability.”—Laura Silverberg
Dominguez, E., Leon, J.I., Montero, C., Marcos, D., Rodriguez, M., Bordons, C., Ridao, M.A., Fernandez, E., 2010. Practical Implementation of an Hybrid Electric-Fuel Cell Vehicle. IEEE Proceedings from the Annual Conference of IEEE, 3828-3833.

Dominguez et al. analyze a practical model of a proposed hybrid vehicle, powered by an array of batteries and a fuel cell. The authors section their data into three main systems that have been integrated into their vehicle design. The first subsection describes the fuel cell power module, the HyPM-XR, which is used in the hybrid vehicle. Like any other fuel cell, this powertrain emits nearly zero emissions other than byproducts such as water and oxygen-depleted air. The fuel cell module, suitable for a wide range of “transportation, stationary and portable applications,” is highly reliable due to its “modular design, fast dynamic response and high efficiency.” The second subsection, focusing on dc/dc boost power converters and auxiliary dc/dc converters, describes the make up of the power electronic system incorporated into the vehicle. The authors make a note of the design system’s weight and volume reduction and that the reliability of this model is achieved by the boost converter system located under the driver’s seat. The converter is also capable of switching frequencies, barely allowing any noise to emit from the vehicle as it comes to a rest, as well as obtaining a dc voltage output higher than its input. If said voltage ratios were higher, a double-boost system could be used. However, the main reason for utilizing the auxiliary dc/dc converter is “to generate the necessary voltage to supply the secondary power systems such as the selenoidal valve and a computer with a tactile screen (PC-car),” as well as provide “300 watts for 20 seconds in the start-up of the fuel cell system.” This PC-car monitoring system, using Labview technology, allows the user to control and monitor the system. This includes the vehicle’s status, “the hydrogen load, the hydrogen pressure, the dc voltage of the fuel cell…the battery stack…and possible warnings and errors.” By providing liberties to the user to manipulate their own hybrid system, the authors’ proposed hybrid electrical-fuel cell vehicle proves to be a good basis and testing platform for future technologies.
In the third and final subsection of the paper, Dominguez et al. describe the proposed vehicle’s control and monitoring system. Hydrogen, an important facet of the vehicle’s design, is stored in the back of the vehicle. The fuel cell uses hydrogen to produce the energy to charge the battery stack when it is needed. When a low battery charge is detected, at a level below 78 volts, the fuel cell injects current to increase the charge. Typically “when a battery charge is applied to a battery stack, its dc voltage increases almost immediately.” On the other hand, when the vehicle is in motion, the dv voltage of the battery stack fluctuates. If this is not taken into account, a simple acceleration of the vehicle could be considered a low battery warning. The authors clarify that as part of their proposed model, this is not a problem since the “controller provides the necessary current to charge the batteries or to drive the dc motor directly.” However, at the same time, there is current flowing from the fuel cell system to charge the batteries. This process can save energy because the battery stack is left unaware that the user “is demanding more power unless the maximum nominal current of the fuel cell system is achieved.” Once the maximum is achieved, the “current from the fuel cell system is saturated and the rest of the power is provided back to the battery stack.”
Dominguez et al. review two experimentally tested scenarios on their proposed hybrid system. In the first experiment, the vehicle “is moving continuously and the driver is accelerating and braking following a hilly path.” Since the fuel cell is providing continuous energy to the battery stack, the battery stack can transfer that energy to the dc motor. In the second experiment, the “vehicle is moving and suddenly…stops.” In this scenario, the fuel cell not only provides power as the vehicle accelerates, but also when the vehicle stops and a low battery level is detected; the fuel cell is prompted to continue providing power in order to charge the battery stack. The authors also found that the vehicle range can be increased from 40 kilometers to 100 kilometers, as the only limiting factor is the hydrogen capacity in the vehicle. Furthermore, all experiments were developed under “real weather conditions.” The authors conclude that in the future, natural park and tourism vehicles should take advantage of their proposed hybrid system. 

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