Nonlinear Dynamics Traction Battery Modeling

This chapter presents a method of determining electromotive force (EMF) and battery internal resistance as time functions, which are depicted as functions of state of charge (SOC). The model is based on battery discharge and charge characteristics under different constant currents that are tested by a laboratory experiment. Further the method of determining the battery SOC according to the battery modeling result is considered. The influence of temperature on battery performance is analyzed according to laboratory-tested data and the theoretical background for calculating the SOC is obtained. The algorithm of battery SOC indication is depicted in detail. The algorithm of battery SOC “online” indication considering the influence of temperature can be easily used in practice by microprocessor. NiMH and Li-ion battery are taken under analyze. In fact, the method also can be used for different types of contemporary batteries, if the required test data are available. Hybrid electric (HEVs) and electric (EVs) vehicles are remarkable solutions for the world wide environmental and energy problem caused by automobiles. The research and development of various technologies in HEVs is being actively conducted [1]-[8]. The role of battery as power source in HEVs is significant. Dynamic nonlinear modeling and simulations are the only tools for the optimal adjustment of battery parameters according to analyzed driving cycles. The battery’s capacity, voltage and mass should be minimized, considering its over-load currents. This is the way to obtain the minimum cost of battery according to the demands of its performance, robustness, and operating time. The process of battery adjustment and its management is crucial during hybrid and electric drives design. The generic model of electrochemical accumulator, which can be used in every type of battery, is carried out. This model is based on physical and mathematical modeling of the fundamental electrical impacts during energy conservation by a battery. The model is oriented to the calculation of the parameters EMF and internal resistance. It is easy to find direct relations between SOC and these two parameters. If the EMF is defined and the function versus the SOC ( 0,1 k∈< > ) is known, it is simple to depict the discharge/charge state of a battery. The model is really nonlinear because the correlative parameters of equations are functions of time [or functions of SOC because ( ) SOC f t = ] during battery operation. The modeling method presented in this chapter must use the laboratory data (for instance voltage for different constant currents or internal resistance versus the battery SOC) that are expressed