The continuous increasing in distributed renewable generation mainly based on wind and solar has complicated recently the normal grid opera-tions. An accurate development in proper energy storage systems with high abil-ity to store and supply energy on demand should effectively eliminate the poten-tially adverse negative impacts of actual grid operation technologies, such as se-vere power fluctuation provided by intermittent power generations and photovol-taic arrays.
The environmental issues impose major changes in actual technologies for vehicle manufacturers. Nowadays, further research is focused on the develop-ment technologies for the vehicles of the future.
Among these technologies the fuel cell hybrid electric vehicle (FCHEV) has an important role due to the poten-tial to improve significantly the fuel economy. FCHEVs can be more efficient than conventional internal combustion engines being an efficient and promising perspective. The lately research was focused on different configurations of FCHEVs, especially in respect to desired hybridization level involving the spe-cific FC and batteries rules for their interconnection. Proton exchange membrane fuel cells (PEMFCs) is regarded as promising candidates for the vehicle applica-tions, mainly due to the mature technology, which can provide electrical power with high efficiency, less noise, compactness, lightness, low operating tempera-ture and very low emissions compared with conventional internal combustion engines.
The electric efficiency usually represents 40-60% while the output pow-er can be changed to meet quickly demanded load. The design of the power source in the FCHEVs is extremely attractive for transport applications. The FCHEV combines the advantage offered by PEMFC with the backup system us-ing the efficient energy management assigned by the Battery.
The LiPo recharge-able battery assures a quick transfer of energy during transient responses and a continuous power during the absence of reactants.
In this chapter we provide a design and energy efficiency analysis for FCHEV implemented in ICSI ENERGY Department, ICSI Rm Valcea, Romania. In order to ensure the required power, an energy management strategy (EMS) has been proposed. The FCHEV performance obtained in simulation using standardized load cycles is validated by taking into account a real experimental speed profile and numerical analysis of the acquired data. This EMS is basically focused on rule-based fuzzy logic control and state machine control. The developed FCHEV is mainly composed of PEMFC stack, LiPo rechargeable battery and DC/AC in-verter. The LiPo rechargeable battery is main energy source, while the PEMFC plays the role of the support system. The feeding of electric motor is assigned by inverter which is able to convert the direct current (DC) in alternate current (AC). The PEMFC supplies the stationary / slow variable load, operating close to the maximum efficiency, and the battery supplies the load transients. Moreover, the PEMFC recharges the battery when is necessary, by considering the available extra energy.
In order to validate the mentioned strategy, we analyzed the efficiency ob-tained by using of the FCHEV in comparison with the efficiency using only bat-tery (electric vehicle). The results indicated more than 90% efficiency in first case in comparison to 75% in the second case, respectively. The reliability of our model was tested and evaluated firstly taking into consideration of various re-sults by using of Matlab / Simulink environment. The experimental study was carried out by considering a specific protocol for extra urban driving cycle (EUDC). Therefore, this chapter takes into account an energy management strat-egy in order to analyze the efficiency obtained by using the FCHEV in compari-son with efficiency by using only battery (electric vehicle).
Keywords: Fuel Cell Hybrid Electric Vehicle; Electric Vehicle; Extra Urban Driving Cycle; Energy Efficiency; Numerical Analysis
A promising solution to provide electricity with zero local emissions in au-tomotive and stationary applications is the fuel cell system (FCS). The most commonly used FCS in hybrid power systems is the proton exchange membrane fuel cell (PEM-FC) due to the high-power density, low volume and low weight compared to other FCs [1,2]. Meanwhile, a lot of research teams are working on new routes for obtaining of hydrogen that uses renewable electricity such as wa-ter electrolysis or various processes of biomass gasification to produce clean electricity [3,4]. In practice, due to sudden changes in the load during the vehicle acceleration phase, improper administration of water management and starvation phenomena with reactant due to the slow response of PEM-FC, leading to loss of performance and cutting down of cycle life [5-7]. Consequently, to eliminate these disadvantages of the PEM-FC mainly due to the slow dynamics, FCs are connected to other power sources (batteries, ultracapacitors) to meet the fast dy-namics of the vehicle’s electric motor [8,9]. Since power is distributed among several sources, it is necessary to establish an energy management strategy (EMS) [10-12].
There are three types of electric vehicles namely: electric vehicles with bat-teries (BEV), electric vehicles with fuel cells (FCEV) and hybrid electric vehi-cles with fuel cells (FCHEV), the last use FC as the main power source and bat-teries / ultracapacitors as auxiliary power source. Fuel cell systems and battery packs have proven to be effective when working together to improve the vehicle efficiency. The main challenge in developing FCHEV is finding an optimal pow-er of FC / Batt / UC for which the efficiency is maximum, as well as establishing of power management algorithms that have as objectives: reducing hydrogen consumption, protecting FC from sudden loads and increasing the lifetime of FC. In this respect is preferable to operate the FC under the most stable conditions and as close as possible to the maximum efficiency point of the FC for a partial charge, while the battery can operate at a high current to remove the FC’s weak points [13,14]. There are numerous recent studies in the literature for the suc-cessful integration of FC into vehicles [11,15-18]. Unlike pure electric vehicles, the battery system in FCHEV can be reduced in capacity, leading to weight loss and lower prices [19,20].
PEMFCs are ideal for automotive applications. The most commonly used catalyst in PEMFC is platinum on carbon due to its good catalytic activity, in-creased durability and corrosion resistance. Platinum is an expensive and rare metal, which is why the PEMFC price is high. However, the high cost of plati-num has led researchers to find alternative solutions to reduce the platinum con-tent by using non-metals [21-23], gold nanacatalysts [24-26] and platinum deco-rated on graphene [27-29]. The specific power of PEMFC used in automotive applications has decreased from 1 kW/kg to 0.65 kW/kg [30]. Fuel cell systems have an efficiency of up to 60% and are capable of providing of a lifetime of 5000 hours, performing 240 000 km, as well as large manufacturing volume in-dicates a cost of $30/kW calculated in the last 3 years [31]. A fuel cell is twice as efficient as an internal combustion engine, and depending on the capacity of the hydrogen tank it can have a range of up to 500 km [32,33].
The energy storage system (ESS) is an important component of an FCHEV. The electric performance of the vehicle depends on the design, storage capacity and type of storage used by ESS. So, depending on the type of vehicle (EVs, HEVs and FCHEVs) the storage system capacity differs, as follows. Normally, EVs must have a higher storage capacity (34.5-140 Wh/kg), while the storage ca-pacity for HEV is lower (26.3-77 Wh/kg) [34], and for FCHEV is between 8.06-18.45 Wh/kg. The ESS capacity for FCHEV must be carefully chosen to meet the starting at low temperatures, variations in energy demands and energy recovery from braking of the vehicle. Thus, choosing the size of storage capacity and ESS hybridization is a challenge for FCHEV producers. Generally, the most used are the Li-ion and ultracapacitor batteries that are used either combined or separate-ly. Another challenge of ESS is performance and robustness.
This chapter is organized as follows. Section 1 presents a short introduction of different configurations of fuel cell hybrid electric vehicles with focus on identi-fying the advantages of attractive challenge for future transport applications. Section 2 presents:
Section 3 outlines the energy management strategy followed by the describing of the system effi-ciencies. Section 4 involves the experimental tests on mentioned component which have been modeled in previous section and their validation. Section 5 pre-sents a detailed analysis of experimental results in respect to electrical vehicle efficiency, all these to demonstrate the strategy?s ability to ensure the required power by involving some improvements for hydrogen consumption and fuel effi-ciency. Section 6 presents the conclusions.
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