## 4 Optimizing Power Flow in EV Powertrains
### Multi-Motor Configuration
Meanwhile, in [88], a fuzzy logic algorithm was applied in the traction distributions on the wheels. The algorithm was responsible to make sure that sufficient traction can be given to each of the wheels to achieve the desired vehicle speed during the driving, while also ensuring that the vehicle trajectory follows the desired driving path. Components of the powertrain used here were optimized using PSO for minimizing the weight of the battery and motors, minimizing drop in the battery's SOC, and reducing driver steering efforts. With the optimized EV powertrain and the fuzzy logic algorithm for the wheels' traction distribution, driver steering efforts can be reduced by 78.5% and the driving mileage can be increased even with the reduced size of the battery. The results obtained in [87; 88] demonstrated the potentials of implementing independent motors for all wheels not only for efficiency but also for the vehicle handling that can possibly contribute in the vehicle safety and autonomous vehicle technologies. For the future scope, the work in [87; 88] can be expanded to evaluate the proposed configuration's performance in controlling the vehicle maneuvering against conventional traction control methods. Summary of the reviewed literature on the multi-motor configurations for EV powertrain is presented in \[T_{out} =\frac{R_{out}}{R_{motor1}}T_{motor1}+\frac{R_{out}}{R_{motor2}}T_{ motor2} \tag{1}\]1 There are two common multi-motor configurations studied in the literature; the two motor configuration, and the four motor configuration. The objective of the two motor configuration is to allow the operation of one motor to be supported by the other motor through either torque coupling or speed coupling. As a result, the operation of these motors can be optimized for diverse driving conditions. The challenge, however, is to come up with the proper mechanism for the couplings, which typically involves multi clutches and brakes. The next challenge will be to effectively and systematically control these clutches and brakes through actuators so that the driving mode shifting can be executed smoothly and efficiently. Regarding the four motors configuration, the objective is to minimize the transmission power loss, since the motor is coupled directly to each wheel. Besides, the traction on the wheels can also be distributed independently, which can improve not only the power consumption, but also the driving stability and safety. Nevertheless, to achieve these, advanced control algorithm is required to integrate effectively the operation of the four motors at the wheels. * To study the application of EV powertrain with two-motor configuration and a four speed AMT. The powertrain was used in a city bus for Nuremberg City Cycle and NYCC. To optimize efficiency and driving comfort by coordinating the gearshifting effectively so that losses and discomfort caused by gear hunting can be avoided. * The proposed powertrain was optimized for minimum total power consumption and minimum 0-40 km/h acceleration time. The control variables were motor scale factor (power ratio of motor 1 to motor 2) and the AMT's four gear ratios. The optimum combinations of the variables were determined using NSGA-II. Three configurations produced from the optimization; Configuration 1 with one motor configuration and two optimized gear ratios, Configuration 2 with two motors configuration with the motor scale factor of 0.42 and four optimized gear ratios, and, Configuration 3 with two motors configuration with the motor scale factor of 1.00 and four optimized gear ratios. Further reads on multi-motor configurations with multi
* Against the typical parallel axle two-motor configuration with single-speed transmission, the proposed configuration yielded faster 0-50 km/h acceleration, but similar 0-100 km/h acceleration rate. The proposal's average efficiency was improved by 2.88% to 8.33% for driving cycles with frequent start-stop. However, the average efficiency was slightly worse (about 0.45%) for the driving cycle with relatively constant vehicle speed.