Thermal Analysis of a Fast Charger for Public Service Electric Vehicles Based on Supercapacitors

Abstract

The aging of supercapacitors (SCs) depends on several factors, with temperature being one of the most important. When this is high, degradation of the electrolyte occurs. The impurities generated in its decomposition reduce the accessibility of the ions to the porous structure on the surface of the electrode, which reduces its capacity and increases its internal resistance. In some applications, such as electric vehicles whose storage system consists of SCs, fast chargers, which supply very high power, are used. This can lead to an increase in temperature and accelerated aging of the cells. Therefore, it is important to know how the temperature of the SCs evolves in these cases and what parameters it depends on, both electrical and thermal. In this contribution, mathematical formulae have been developed to determine the evolution of the temperature in time and its maximum value during the transient state. The formulae for obtaining the mean and maximum temperature, once the thermal steady state (TSS) has been reached, are also shown, considering that the charger cells are recharged from the grid at a constant current. Based on this formulation, the thermal analysis of a specific case is determined.