Abstract
Electric cars are typically subject to highly variable operational conditions, especially when they drive in urban environments. Consequently, the efficiency of the electric motors may degrade significantly, possibly leading to lower autonomy and higher running costs. Latest advances in power electronics and motion control have paved the way to the development of novel architectures of full electric power transmissions. In this paper, a dual-motor solution is proposed where two smaller motors are coupled via a planetary gear, in contrast to the standard configuration that uses one larger motor directly connected to the drive wheels with a fixed ratio reducer. The dual-motor architecture guarantees that both motors operate in the vicinity of their optimal working range, resulting in a higher overall energy efficiency. The technical requirements and the control strategy of the dual-motor system are selected through a parametric optimization process. Results included were obtained from extensive simulations performed over different standard driving cycles, showing that the dual-motor power transmission generally outperforms the single-motor counterpart with an average efficiency improvement of about 9% that is reached in both the power delivery and regeneration stage.
Highlights
Full-electric vehicles (EVs) are increasingly attracting attention as they promise to offer advantages over traditional internal combustion engine vehicles in terms of environmental impact and improved efficiency [1]
One of the main challenges refers to the limited autonomy that can be obtained through the development of efficient transmission systems and their integration with existing EV powertrains
Electric motors can be directly connected to the drive wheels of EVs, or a transmission system can be placed between the motor and the wheels to optimize the vehicle performance [2]
Summary
Full-electric vehicles (EVs) are increasingly attracting attention as they promise to offer advantages over traditional internal combustion engine vehicles in terms of environmental impact and improved efficiency [1]. The main contributions of this research are: (i) evaluation of the increase in the energy efficiency of the proposed powertrain over different standard drive cycles; (ii) definition of the optimal nominal requirements of the planetary gear and electric motors; (iii) a control strategy to set the operating condition of the two electric motors in order to maximize the efficiency of the powertrain. We investigate the use of a planetary gear for the power transmission of full electric vehicles with the aim to uncouple the speed range of two electric motors from that of the car and keep both electric machines in their optimal efficiency window
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