I. Introduction
Electrical machines are the heart of many modern appliances, as well as industry equipment and systems. In a global market and in the context of sustainability, they must fulfill various requirements physically and technologically. To satisfy these requirements, optimization is of great significance for electrical machine design, and many optimization methods have been developed. Optimization methods mainly include the following: 1) direct optimization of analysis models, such as analytical model, magnetic equivalent circuit model, and finite-element model (FEM), and 2) indirect optimization of approximation models (surrogate models of FEM), by using different kinds of optimization algorithms including intelligent algorithms. Some popular intelligent algorithms are the genetic algorithm (GA), the differential evolution algorithm (DEA), and the particle swarm optimization (PSO) algorithm. Surrogate models mainly include the parametric models, such as response surface model (RSM) and radial basis function (RBF) model; semiparametric model, e.g., Kriging model; and nonparametric models, such as artificial neural network and support vector machine models [1]–[8] .