Integrated Design of a CVT-equipped Electric Powertrain via Analytical Target Cascading

Abstract

Electric vehicles are gaining momentum as a valid alternative to conventional engine-based cars. In order to meet the high expectation of the market, they must strive for a similar, if not better, performance and driving range. To this end, their powertrain must be carefully designed and account for the interconnections among the various components in an integrated fashion. In this paper, we present a co-design framework for electric powertrains, whereby we jointly optimize the size of the electric machine (EM) and the geometry of a continuously variable transmission (CVT) together with its ratio trajectory, with the goal of minimizing the energy consumption of the vehicle. Specifically, we first frame the minimum-energy co-design problem in an integrated manner, accounting for the CVT geometry and dynamics, and the EM size. Given the problem complexity, we decompose it into an EM-design and a CVT-design subproblem, whereby we jointly optimize the CVT-ratio trajectory, and leverage analytical target cascading (ATC) to effectively solve the design problem. Finally, we showcase our framework on the New European Driving Cycle (NEDC), highlighting the importance of designing powertrains in an integrated fashion: Compared to the case whereby only the EM, the CVT, or the control are optimized, our joint EM-CVT design can improve the energy consumption of the vehicle by up to 22%.