## 3 Numerical Modeling and Novel Technologies and Materials  
### Drives and Electric Vehicles  
The electrical machine is one of the main component in many different electrical energy drive and conversion systems. These systems use more than 53% of the consumed electricity in the different sectors of the industry [220], which means about 6040 Mt of CO2 emissions per year. Due to global sustainability, the electrical drive systems have to fulfill more and more rigorous requirements, not only physically and technologically, but also environmentally [167]. Each electrical drive system, besides electrical machines, also includes power electronic devices, control systems, and other protection and mechanical subsystems, as illustrated in Figure 9. The integral optimization of electrical drive systems to productively maximize overall efficiency typically includes the application of more efficient and well-sized components [221]. Both the research and industry communities are highly interested in the design and optimization of electrical drive systems, especially in the field of Electric Vehicles (EVs). Research practice shows that the system-level design part plays a significant role in development. Due to the non-linearity of the whole system, it is more valuable to follow the optimal performance of the whole drive system rather than pick up excellent separate components (e.g. power electronics, electric motor, or gear), and usually, assembling of such individually optimized single components into a complete drive system cannot ensure the best performance [222]. For example, extra harmonic losses can appear in the electrical machine due to the harmonic distortion in power electronic devices. The loss analysis methodology must be applied to the  
Figure 8: An example of a false minimum in the surrogate model. holistic drive system to ensure that reducing losses in a single component will not have a negative effect on the efficiency of the other parts. and vice versa [223]. Due to the high time requirements and costs, only a limited number of electrical drive system components have been redeveloped recently [224]. Rather, the actual components are slightly modified and adapted to new applications. [PERSON] et al. [222] suggested a five step design optimization framework for the EV electrical drive, as follows:  
* determination of electrical system requirements (e.g. cost, efficiency, speed range, controllability, power density, electrical machine torque, etc. );
* topology selection;
* design of the electrical machine and/or power electronics device;
* optimization of designed parameters. * evaluation of the whole electrical drive system's performance, including the steady-state performance and dynamic response. However, this methodology decomposes the optimization task into a separate machine and electronic device design, as two parallel, independent optimizations. Therefore, this methodology can give a good practical design in a reasonable time, but cannot ensure (mathematically) that the found optimum is the global optimum of the whole electrical drive system. In other studies by [PERSON] et al. [167; 225; 226; 227], a robust approach for the system-level design optimization of the electrical machine and drive system based on Design For Six Sigma (DFSS) was presented. DFSS allows using empirical data, and it is based on the use of statistical tools. Certain case studies (including multiobjective and system-level optimization) on a PM transverse flux machine with a soft magnetic composite material core were investigated by the authors. Based on the studies, it may be highlighted that the electrical drive system's reliability may be consequently improved by a robust design optimization approach. This fact may extend the industrial application area of the drive system and benefit manufacturing. However, for this DFSS methodology, as for the Taguchi method, designed for discrete parameters, it is difficult to handle wide and continuous parameters and a large number of constraints. [PERSON] et al.