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1. Introduction
Synchronous reluctance machines (SynRMs) are gaining more attention in applications requiring high dynamics, high torque density and fault-tolerant capabilities, such as traction and household appliances (Bianchi et al., 2022; López-Torres et al., 2018). Robust rotor structure, absence of rotor joule loss, low cost and convenience in manufacturing are the advantages of a SynRM (Cai et al., 2016; Wang et al., 2015). As the SynRM rotor is made of iron lamination, no brushes/slip-rings and expensive permanent magnets are needed (Cai et al., 2014, 2016). Although electrical machines with rare-earth permanent magnets have high performance, the high cost and the insufficiency of rare-earth permanent magnet materials will be obstacles to further development in applications such as electric vehicles or hybrid electric vehicles (Liu et al., 2016; López-Torres et al., 2018). Line-start synchronous reluctance motors are also a suitable alternative to induction motors in fixed-speed direct-on-line applications such as pumps and fans (Baka et al., 2021; Hu et al., 2022).
In a SynRM, the total developed electromagnetic torque is the reluctance type. Therefore, the rotor shape optimization is crucial in designing SynRMs because the machine performance is directly proportional to the rotor’s magnetic saliency ratio. In the case of an improper design, a SynRM presents some drawbacks, such as a high torque ripple and a low-power factor (Bianchi et al., 2022; Cai et al., 2014). The rotor geometry in SynRMs is complex, and many geometrical parameters are involved (Bacco and Bianchi, 2019). Several flux-barrier layers per pole should be taken into account to achieve a good magnetic saliency ratio (Wang et al., 2017; Guan et al., 2016). This, in turn, makes the rotor optimization process a difficult task because in an optimization problem, when the number of decision variables is high, the number of objective function calls increases.
Figure 1 shows some possible rotor topologies to generate reluctance torque for a continuous rotation. As you can see, these structures aim to generate an appropriate non-uniform permeability distribution in the rotor to generate reluctance torque. Figure 1(a) represents the rotor geometry of a switched reluctance machine. In this machine, the rotor magnetic anisotropy is achieved by salient poles. Figures 1(b) and 1(c) show two...