Abstract
Electric vehicle (EV) traction drives should be associated with flux-weakening (FW) techniques wide-range speed demands. In this study, the EV performance with an optimal FW strategy is studied in relation to the battery voltage variation caused by cell state-of-charge and temperature changes. The results show that the battery suffers from a voltage reduction by larger internal resistance as the temperature decreases. Moreover, the higher current is required for activating the FW process. However, the inner resistance growth produces more heat inside the cell that affects the battery electrical parameters as well as the system. To assess this effect by simulation, an improved electro-thermal model of lithium-ion battery ls dynamically coupled to the optimal FW strategy. In this model, all the electrical parameters are temperature-dependent deduced from experimental measurements of an off-road EV. The simulation results confirm the effect of the cell self-heating on the battery voltage at sub-zero temperatures. The higher battery voltage can support the FW operation at −10°C for more 1200 s under the modified NEDC driving cycle, whereas the motor drive voltage is saturated after 1118 s by using the simple battery model without thermal effects.
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