Optimizations of a permanent magnet machine targeting different driving cycles for electric vehicles

Abstract

The paper assesses the influence of driving cycles on the design optimizations of permanent magnet machines for electric vehicle traction applications with the objective to minimize total loss over a defined driving cycle while satisfying performance specifications and design constraints. With the help of an efficient optimization methodology and tool, the optimizations against New European Drive cycle (NEDC), Artemis Urban Drive Cycle (Artemis), and the NEDC/Artemis combined cycle are carried out using Finite Element (FE) based technique. It is shown that for a surface mounted permanent magnet machine studied in the paper, the optimization results against the NEDC and Artemis exhibit distinct characteristics in terms of torque, speed, and energy loss distributions. Thus optimization trends for leading machine design parameters such as split ratio, stator tooth width, turn number per coil and magnet usage to minimize total loss for NEDC and Artemis are very different. For NEDC, the optimum design inclines to reduce high-speed copper loss and iron loss; for Artemis, it tries to minimize low-speed copper loss. Comparing the three optimized motors targeting different driving cycles, it is observed that they all have very high efficiency over a wide toque-speed range, and perform the best in their own target cycle, and with around 0.5% lower efficiency, or 10% higher loss in the other cycles with respect to the optimum values. Compared to the motor optimized for Artemis, the motors optimized against NEDC and the combined cycle result in close to 20% less magnets and less copper usage, making NEDC or the combined driving cycle a preferred optimization target.