Disruptive innovations in electrical machine design optimization are observed in this paper, motivated by emerging trends. Improvements in mathematics and computer science enable more detailed optimization scenarios that cover evermore aspects of physics. In the past, electrical machine design was equivalent to investigating the electromagnetic performance. Nowadays, thermal, rotor dynamics, power electronics, and control aspects are included. The material and engineering science have introduced new dimensions on the optimization process and impact of manufacturing, and unavoidable tolerances should be considered. Consequently, multifaceted scenarios are analyzed and improvements in numerous fields take effect. This paper is a reference for both academics and practicing engineers regarding recent developments and future trends. It comprises the definition of optimization scenarios regarding geometry specification and goal setting. Moreover, a materials-based perspective and techniques for solving optimization problems are included. Finally, a collection of examples from the literature is presented and two particular scenarios are illustrated in detail.

A novel rotor structure for a tooth-coil-winding (concentrated winding) open-slot axial-flux permanent-magnet (PM) machine that reduces the eddy currents and increases the main flux linkage is proposed in this paper. A composite-body-based rotor assembly and a steel-laminated layer inserted on top of the magnets are used to reduce eddy-current losses in the PMs. A prototype of an axial flux generator for a heavy-duty vehicle following this structure is optimized, analyzed and measured. The tooth coil windings produce high-amplitude harmonics in the air gap and the large slot openings reduce the rotor flux. Consequently, a rotor structure that decreases the amount of harmonics travelling through the magnets is required. Steel laminations covering the magnets have positive effects on both phenomena. Two-dimensional and three-dimensional finite-element analysis is used to verify and optimize the geometry of the laminations. Computations are verified by experimental measurements of a 100 kW test machine prototype.

This Special Section on "Optimization of Electrical Machine Designs" summarizes the state-of-the-art on the latest researches carried out on the topic, both in the academic and industrial environments. Basically, all the electrical machine topologies and optimization techniques have been discussed in this Section, suggesting to the readers interesting solutions of several optimization problems related with modern applications. The second part of the special section (the first one has been published in the December 2017 issue of the IEEE Transactions on Industrial Electronics) includes 20 papers from a total of 44 accepted contributions. The studies included in the Part II are categorized in a table and are outlined to some extent in order to help the readers to quickly compare the main peculiarities of the mathematical approaches and the practical implementations. The Part II paper categorization of this Special Section presents a second set of four papers focused on the permanent magnet synchronous machines

This paper presents a methodology for the analytical computation of the slot leakage inductance of tooth-coil winding (TCW) permanent magnet synchronous machines (PMSMs). Generalized equations for the slot leakage inductance of the whole phase are derived, suitable for several slot-pole combinations, and meant to be used during the machine design stage. For simplicity, self- and mutual-inductance components are formulated using the classical method with detailed permeance determination for both horizontal and vertical distribution of coil sides in the slots, considering a straight-line path for the flux leakage. Several slot-pole combinations were simulated by means of Finite Element (FE) method in order to validate the analytical equations, both approaches, FE and analytical, showing adequate concordance.

Thermal modeling of a 100 kW radial flux permanent magnet electrical machine is studied and verified by experiments. The traction machine has hybrid cooling. A simplified thermal model based on Computational Fluid Dynamics (CFD) was used to analyze the temperature distribution throughout the machine. The machine has a water jacket and adopts potting materials around the end-windings. The potting materials around the end windings operate as heat paths to the frame coolant. The design principle of the cooling system is presented in details. Experimental investigations are performed on a 100 kW radial flux permanent magnet electrical machine to validate the simulation results.

This paper analyzes the impact of manufacturing tolerances on the cogging torque of a 24-slot 28-pole tooth-coil-winding permanent magnet synchronous machine with a modular stator core (TCW-MPMSM). Dimensional tolerances and asymmetries associated with the modular topology are studied by means of finite element simulations in order to identify key parameters that increase the cogging torque above the expected values of a faultless machine. Among five selected dimensional parameters, it was found that angular displacement, radial displacement, and tooth–tip width deviations of the stator segments have the most significant impact on the cogging torque. Considering these three key parameters, a full-range tolerance analysis is carried out by means of a proposed superposition-based approach, evaluating all possible combinations of typical deviation values. It is concluded that the cogging torque increment, generated by tolerances, is relatively independent of the faultless tooth–tip width of the stator segments and the arc-to-pole ratio. Robustness of the TCW-MPMSM, regarding cogging torque generation, depends on both the tightness of the tolerances handled in the manufacturing process and the rated cogging torque: the lower the cogging torque of the ideal machine, the less robust is the machine and, therefore, manufacturing imperfections will be required to be tightened.