BEV Powertrain Component Sizing With Respect to Performance, Energy Consumption and Driving Patterns

Licentiate thesis, 2014

In this thesis, various drive cycles, legislative, official real-world and measured within the frame of the project, have been studied and characterized in terms of speed and acceleration cycle parameters, as well as acceleration and speed distribution. The objective was to assess typical vehicle usage on different road types, but also to study the implication on vehicle energy consumption due to the drive cycle’s characteristics. For this evaluation, three reference vehicles were designed after different set performance requirements, with data on existing BEVs as a frame of reference. An available traction motor, power electronic module and battery cell were utilized, where the motor was scaled by active length. Finally, the consequence of downsizing the electric drive system in terms of energy consumption and performance was also studied. Through comparison between legislative together with official real-world cycles and measured drive cycles, it was found that even though the measured cycles reach higher peak acceleration levels for a certain speed level, they still spend only slightly more time at higher levels of acceleration compared to the official cycles, at least on average over a group of similar cycles. During the powertrain sizing regarding torque and power, it turned out that the acceleration requirementwas dominating over other requirements such as top speed, and grade levels. The analysis shows that for two cycles with similar speed parameters such as maximum and average speed and time share at low speed, but where the speed time traces are very different with many more speed fluctuations in one cycle compared to the other, in combination with generally higher acceleration levels, the increase in net battery energy consumption per distancemay be as high as 28% for the cycle with more speed fluctuations. By down-scaling the electric drive system of the City car by 40%, the net battery energy per driven distance for low speed cycles increased by about 3−6%, while three of the cycles could not be fulfilled due to limited acceleration capability.