Design and Validation of Ultra-Fast Charging Infrastructures Based on Supercapacitors for Urban Public Transportation Applications

Abstract

The last few decades have seen a significant increase in the number of electric vehicles (EVs) for private and public transportation around the world. This has resulted in high power demands on the electrical grid, especially when fast and ultra-fast or flash (at the bus-stop) charging are required. Consequently, a ground storage should be used in order to mitigate the peak power request period. This paper deals with an innovative and simple fast charging infrastructure based on supercapacitors, used to charge the energy storage system on board electric buses. According to the charging level of the electric bus, the proposed fast charging system is able to provide the maximum power of 180 kW without exceeding 30 s and without using DC–DC converters. In order to limit the maximum charging current, the electric bus is charged in three steps through three different connectors placed between the supercapacitors on board the bus and the fast charging system. The fast charging system has been carefully designed, taking into account several system parameters, such as charging time, maximum current, and voltage. Experimental tests have been performed on a fast charging station prototype to validate the theoretical analysis and functionality of the proposed architecture.

Characterization and Model Parameters of Large Commercial Supercapacitor Cells

“…The tests at constant current with high current value are relevant for applications of SCs in energy storage. The manufacturers normally suggest to limit the operating cycle of the cells to span a voltage range between the rated voltage Vr and the 50% of this value, corresponding to a usable energy of 75% of the maximum storable energy [5], [9]. This voltage range was used in the tests.…”

“…For these reasons, they found a wide range of applications in transportations, in industrial systems and in electric power grids. In particular, SCs are exceptionally effective when repetitive pulsed power is required [3], [4]- [5]. Furthermore, the integration of SCs into hybrid solutions, like their combination with energy-intensive sources as lithium-ion batteries, appears as the potential key approach for future flexible and cost-effective energy storage devices or systems [1], [4], [6]- [9].…”

Design and Implementation of Reduced Grid Impact Charging Station for Public Transportation Applications

“…The right choice of the power converters' topologies and the selection of the power semiconductors are the key factors in improving the efficiency and the power density of the charging units [12,13]. In [14] the electric bus was equipped with a pantograph in order to test the Flash Charge (at the bus stop), as illustrated in Figure 1.…”

“…The right choice of the power converters' topologies and the selection of the power semiconductors are the key factors in improving the efficiency and the power density of the charging units [12,13]. In [14] the electric bus was equipped with a pantograph in order to test the Flash Charge (at the bus stop), as illustrated in Figure 1. In this paper, to properly design a new onboard storage system, the information about the route of the electric bus including its energy consumption is absolutely needed [15][16][17].…”

A Flash Charge System for Urban Transport

“…With a direct connection between charged and discharged capacitors, inrush currents are relatively high (thousands of amperes). So the designers of the passive recharge station (which was managed by the research team of Prof. Lidozzi of Roma 3 University) adopted a configuration visible in figure 6 [5]. An inductor is used in order to smooth current derivatives (power stored on peak currents is smoothly recovered during the final part of the recharge).…”