BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI

106 Vlad Marţian et al
there is also the advantage of efficiency which for the electric engine is around
80% -90%.
The main obstacle in producing on a mass scale this type of vehicles is
represented by the storing capacity of the electrical energy i.e. the batteries.
Actually the storing capacity is not enough, so one of the main directions of
research is to improve the storing capacity of the batteries. This increase in
energy density and also the need for drawing high powers form the batteries has
another side effect such as increasing the temperature of the battery. The
working temperature of the battery is a very important parameter, for example
for a Li-ion cell an increase in temperature of 15°C will reduce the life of the
cell by about 50% (Asakura, Shimomura & Shodai, 2003). The temperature has
also another effect on the charge/discharge of the battery and also on the storage
capacity of the battery. These parameters i.e. charge/discharge and storage
capacity is quantified by using the term SOC (State of charge). In the work of
Zheng Popov and others (Zheng, Popov & White, 1997) an optimum
temperature for a battery is around 25°C, even if now there are batteries that can
have a maximum temperature of 85°C (Winston, 2011). The current
discharge/charge rate grows as the temperature approaches the optimum due to
increased ion mobility and also due to modifications of internal resistance of the
battery, but after the optimum the current charge/discharge rate stats to decrease
due to oxidations that happen inside battery. Increasing the temperature over the
functioning domain make the batteries to have a catastrophic failure, and not
only the performance of the battery will be diminished but also irreversible
oxidations occur and the battery becomes useless (Jiangang, et. al., 2006).
For these reasons, toghether with RAAL S.A., we began to investigate the
necesity of a cooling system for batteries equiped in EV and HEV. This paper
presents the first step from many that includes battery modelling, the modelling
of cooling modules, the modelling of an automatic driver, experimental tests of
the cooling modules, and thermal test on the battery pack, etc.
2. Battery Models
The literature has many models which vary in complexity. There are
complex models that use quantum mechanics for describing the battery at
chemical reaction level (Parthasarathy et. al., 2002), (Aron, Girban & Pop,
2010), finite element models that describe the spatial dynamics in the battery
(Sievers, Sievers & Mao, 2010),electrochemical models, electrical equivalent
circuit (Matthias et al., 2005), Dynamic Lumped parameters models, tabulated
battery data models.
To model the battery as close to the reality as possible every model has to
take into account the parameters on which the battery depends on, and these
parameters are a few. One of the most important parameter that the battery has
is the so called state of charge, SOC, or the electrical energy stored in the
battery. This parameter depends on other parameters of the battery as the