Novel powertrain topologies for energy-efficient battery electric vehicles

Licentiate thesis, 2023

The global transition towards sustainable transportation has underscored the importance of battery electric vehicles (BEVs), with a growing need for enhancement in powertrain energy efficiency to mitigate range anxiety and promote widespread adoption. In response to this need, there have been significant contributions from advancements on powertrain components, such as electric motors and inverters, towards increased energy efficiency. However, it is crucial to acknowledge that BEV powertrain efficiency is not simply a product of the efficiencies of electric motors and inverters. In this context, the exploration of novel powertrain topologies presents itself as an alternative and promising approach for further enhancing BEV powertrain efficiency. Moreover, when component-level advancements are integrated with innovative powertrain topologies, there is potential to push the boundaries of powertrain energy efficiency in BEVs.

To this end, system simulation techniques are utilized in this thesis to evaluate different powertrain topologies in terms of energy efficiency over standard drive cycles, each operating under its optimal powertrain strategy. Specifically, two powertrain topologies are investigated in this thesis: 1) the Adaptive Front- and Rear-Axle Independently Driven (AFRID) powertrain features two clutches that enable the mechanical disconnection of two electric motors with differentiated high-efficiency operating areas, aiming to address the inherent high no-load losses of dual motor powertrains while utilizing the high-efficiency zone of each motor and leveraging torque distribution functionality to enhance overall efficiency. 2) The adjustable DC-link voltage powertrain allows the adjustment of DC-link voltage to an efficiency-favored level irrespective of the battery voltage, in response to dynamically changing driving conditions.

The findings of this thesis indicate that the integration of both investigated powertrain topologies with state-of-the-art components can significantly enhance powertrain energy efficiency in comparison to conventional BEV powertrains. Importantly, these improvements in efficiency do not come at the expense of vehicle performance or driveability; in fact, vehicles equipped with these novel powertrain topologies are observed to exhibit superior performance and improved driveability, making them highly favorable options for the next generation of BEV powertrains.