## 2 Preliminary Results and Research Methodology  
The first step in developing a fully functional electric drive system for a light electric vehicle (L6 European class) was to determine the drivetrain topology that is best suited for this type of application. An in-depth study was performed [24], focusing on an evaluation of the configurations already used in commercial EVs: (a) a single electric machine (EM) connected to the wheels through a mechanical system consisting of a combination of gearbox, differential, and drive-shafts; (b) two in-wheel outer-rotor EMs; or (c) two EMs directly connected to the vehicle wheels (Figure 1). The study revealed that the latter topology had the best efficiency while operating on an NEDC cycle limited to 45 km/h. However, if other factors were considered, such as the technological challenges of the in-wheel structure, the cost of the additional electronic converter required for the second EM, or the different rotational speed of the two EMs while cornering, the best solution seemed to be the former. The study also included a comparison of several PMSMs rotor topologies, considering several interior-PM structures, showing that the spoke variant had similar results to other structures that were considerably harder to build and more expensive. A study on two variants of PMSMs suited for this application was performed [25], considering two topologies with three-phase, 15 slots, stators, and four-pole rotors with spoke and interior PM arrangement. The statoric winding is a two-layer distributed configuration, as shown in Figure 2a,b. A multi-objective optimization, using the genetic algorithm (GA) technique available in JMAG software, was implemented with the aim of increasing the efficiency of the machines. During the optimization process, different geometric dimensions were varied in order to maximize the efficiency, to minimize the electromagnetic torque ripples, and to maintain the maximum value of the magnetic flux density bellow 1.8 T through the stator core, to avoid saturation. The objective function, to be maximized, is highlighted in the following relation:  
\[f=eff*0.4+\frac{T_{rip\ i}}{T_{rip}}*0.2+\frac{1.8}{B_{st\ tech}}*0.2+\frac{1.8}{B_{st\ \ yoke}}*0.2 \tag{1}\]  
Figure 1: Studied drivetrain topologies: (**a**) single EM with mechanical transmission, (**b**) in-wheel outer rotor EM, (**c**) EM directly connected to the wheels. where:  
\(eff\)--motor efficiency;  
\(T_{rip}\)--torque ripple;  
\(T_{rip}\) --torque ripple for the initial case;  
\(B_{st\text{ }teelth}\)--magnetic flux density in stator teeth;  
\(B_{st\text{ }yok}\)--magnetic flux density through stator yoke. The optimization process was performed for a rotor speed of 4200 rpm and a phase current of 145 A. After the optimization phase was concluded, two efficiency maps, one for each machine, were obtained from simulations (Appendix A, Figure A1) considering a speed operating range from 0 to 4500 rpm. For a better comparison between IPM and spoke-type machines, the stator geometries and PM volumes were considered identical; the results of the study (Table 1) showed that the two PMSM had similar performances. The interior PM structure exhibited better efficiency due to smaller iron losses since it used less lamination material in the rotor. Both topologies were built; however, the current article focuses on the spoke-type PMSM. After the prototype spoke-type PMSM was built, several tests were made to determine the electrical characteristics and behavior of the machine. In Figure 3, a comparison between