## 4 Optimizing Power Flow in EV Powertrains
### Multi-Motor Configuration
With the difference of only 0.63% in terms of efficiency gain between the first and the third configurations, it was logical to choose the first configuration for an actual implementation. Therefore, in the future work for [78], more studies can be carried out to compare the driving and gearshifting performance of these configurations so that more aspects can be evaluated. Figure 15: (**a**) First, (**b**) second and (**c**) third two motors EV powertrain configurations proposed in [78]. Next, in a latest work described by [79], a two-motor configuration based on a [PERSON] planetary gearset was proposed in a two-motor EV powertrain configuration. Unlike the configuration described in [78], this proposal provided two gear ratios in the powertrain, resulting in more flexibility for the driving modes. The [PERSON] planetary gearset consisted of two planetary gearsets with a brake for each set's ring gear, and another brake was used at the first motor's shaft. The ring gear of the first planetary gearset was connected to the second motor, and the ring gear of the second planetary gearset was connected to the first gearset's planet carrier. The planet carrier of the second gearset, on the other hand, was connected to the wheels through a differential, while the sun gears of both planetary gearsets was connected to the first motor. Figure 16 depicts the diagram of the [PERSON] planetary gearset configuration proposed in [79], which was capable of providing six driving modes (two modes with two motors, and four modes with one motor). The two modes with two motors represented the possibility of torque coupling and speed coupling of the motors, and the four single-motor modes represented the power flow from the first and second motor through two-speed gear ratios. The powertrain configuration's motor power and gear ratios were optimized using GA for minimum average efficiency in six driving cycles (LA92, JP1015, NEDC, WLTP and HWFET), high gradeability (40% at 10 km/h), high top speed (at least 190 km/h) and fast 0-100 km/h acceleration time (at around 10 s). The proposal was then compared with the typical parallel axle dual motor configuration with fixed gear ratio for evaluation. In terms of acceleration, the proposal provided faster 0-50 km/h acceleration time, but no significant difference was observed for the 0-100 km/h. For the average efficiency, the proposed Simpson planetary gearset configuration was more efficient than the typical parallel axle dual motor configuration by around 2.88 to 8.33% when employed in driving cycles with frequent acceleration and deceleration. However, in a driving cycle with relatively constant vehicle speed (like HWFET), the typical configuration was slightly more efficient by 0.45%, very likely due to the losses in the planetary gearsets. Moreover, the proposed configuration also required three actuators for the three brakes to properly control coupling between the two motors. In this aspect, advanced control algorithm for the actuators is crucial to ensure that they can be operated systematically not only for powertrain efficiency but also for driving comfort by minimizing the jerking during the driving mode shifting. Thus, in the future study, it is imperative to evaluate the workability and control of these actuators so that their performance in terms of powertrain efficiency, jerking and shifting time can be quantified and compared. Figure 16: (**a**) Proposed two motors powertrain configuration with Simpson planetary gearset and (**b**) the typical parallel axle two motors configuration [79]. The subsequent work on multi-motor configuration is described in [80], which like [79], studied the possibility of applying an EV powertrain with a two motor configuration and a multispeed discrete transmission, in this case four speed AMT. The powertrain was applied in a city bus for a specific Nuremberg City Cycle and also for NYCC, where the focus was to optimize the driving strategy by properly coordinating the gearshifting.