Comparison of two Different Electrical Power Architecture for Electric Vehicles Applications Based on Fuel Cell and Supercapacitors
Abstract
The use of Fuel Cells as main source of energy is being extended to automobile applications, due to their good performance. However, Fuel Cells cannot fulfil with strong load requirements produced during the vehicle operation. So, a secondary energy source must be used in order to provide fast changes in the current load, and to store the reverse current generated by the load, if regenerative braking is intended. This work compares two different electric power distribution architectures which share a double objective. On the one hand, the regenerative energy produced during the brake has to be stored and on the other hand, the DC Bus voltage that is applied to the electric engine, in order to move the vehicle wheels, has to be controlled and regulated. The difference between the two studied architectures is related to the secondary source of energy used in order to fulfil the goals of the system. The secondary energy source can be either Batteries or Supercapacitors. As a result of the behaviour comparison of both architectures, the best application field for each one is determined, as well as their advantages and disadvantages. Finally, this paper analyzes the influence that the kind of urban profile applied and the possibility of regenerative braking have over the whole system. Keywords: Fuel Cell, Supercapacitor, regenerative braking, electric vehicle, Bidirectional converter.
I. INTRODUCTION
Fuel Cells are considered as one of the distributed energy sources with most potential, due to their reliability and the generation of non damaging emissions for the environment [1]. Moreover, because of their scalability they can be used in very different applications. Particularly, the use of Fuel Cells has been extended to automobile applications. Electric Vehicles powered by Fuel Cells, as main source of energy, provide better performance than vehicles powered by batteries. This is mainly because of the limited driving range, low life time and high maintenance cost of the batteries [2]-[3]. However, the automobile operation requirements can present fast changes, depending on the travel mode, which cannot be attended by Fuel Cells, due to their slow dynamic response. In addition, they cannot accept reverse current, and they provide a relative low output voltage that depends on both, output current and age [1]. Summarizing, in most applications is needed the use of a secondary energy source capable of delivering high currents to the load, and to store the reverse current from the load, if regenerative braking is intended. This work presents the comparison of two different electric power distribution architectures, which share a double objective. On the one hand the regenerative energy produced during brake has to be stored, and on the other hand the DC Bus voltage has to be controlled and regulated.


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