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Battery sizing has significant importance for the performance of hybrid electric vehicles (HEVs). Although several research has been done over the years for the battery sizing, no research has focused on battery system efficiency which affects fuel economy. This paper has investigated battery system efficiencies of different optimum battery sizes which were optimised using two design optimisation methodologies. The first methodology considered a single driving pattern at a time, whereas, the second methodology considered different driving patterns simultaneously for the optimisation. The study considered a simulation model of a power-split HEV for the optimisation of battery size along with internal combustion engine, motor, and generator. An electric-assist charge sustaining supervisory control strategy was considered as the energy management. The maximum speed, acceleration, and gradeability were considered as design constraints.

The power demand of air conditioning in PHEVs is known to have a significant impact on the vehicle’s fuel economy and performance. Besides the cooling power associated to the passenger cabin, in many PHEVs, the air conditioning system provides power to cool the high voltage battery. Calculating the cooling power demands of the cabin and battery and their impact on the vehicle performance can help with developing optimum system design and energy management strategies. In this paper, a representative vehicle model is used to calculate these cooling requirements over a 24-hour duty cycle. A number of pre-cooling and after-run cooling strategies are studied and effect of each strategy on the performance of the vehicle including, energy efficiency, battery degradation and passenger thermal comfort are calculated. Results show that after-run cooling of the battery should be considered as it can lead to significant reductions in battery degradation.

Among the auxiliary systems on electric and hybrid electric vehicles the electric air conditioning (eAC) system causes the largest load on the high voltage battery and can significantly impact the energy efficiency and performance of the vehicle. New methods are being investigated for effective management of air conditioning loads through their integration into vehicle level energy management strategies. For this purpose, a fully integrated vehicle model is developed for a commercially available hybrid vehicle and used to develop energy management algorithms. In this paper, details of the eAC model of this vehicle are discussed, including steady state component validation against rig data. Also results of simulating the cabin pull-down are included.