## 1 Introduction  
In safe-critical applications, the uninterrupted and reliable operation of the electrical machine is requisite, which is described by their fault-tolerance capability. This is the case, for instance, of aeronautical, aerospace, and electromobility applications [1; 2; 3]. As a concept, fault-tolerant machines should provide acceptable levels of electric, magnetic, physical, and thermal isolation of phase windings [3], and can also consider multiphase windings [4; 5] or limiting short-circuit current capability [6; 7]. In addition to the fault-tolerance capability, electrical machines must provide enough power density, efficiency, and electromagnetic performance to meet the application's requirements. In this regard, electrical machines based on permanent magnets (PMs) are well known as the most promising technology in terms of power density and efficiency [8; 9; 10; 11], but they lack inherent fault-tolerance capability [12]. It is desirable that PMSMs resist winding open-circuit and short-circuit faults without compromising the integrity of magnets. Nevertheless, since their electromagnetic performance is unmatchable by other conventional topologies so far, considerable efforts have been carried out in the last few years to enhance the fault-tolerant capability of PM machines [2; 3; 4; 5; 7; 12; 13; 14]. In the technical literature, adopting a modular stator core, as illustrated in Figure 1b, has been shown to be a feasible solution to enhance the fault-tolerant capability of PM machines [15; 16; 17; 18; 19; 20; 21; 22; 23]. This obeys mechanical and electromagnetic reasons, since PM synchronous machines with modular stator core (MPMSMs) offer several advantages in high-power density and fault-tolerance applications [15]: they can provide physical, thermal, and electromagnetic insulation between phases, lower material requirements (laminations) than conventional topologies and a high slot fill factor [16]. Notwithstanding, the cost of MPMSMs developing these features is the presence of manufacturing and assembly challenges, decrease in mean torque, and increase in torque ripple [15; 18; 19]. As can be seen from Figure 1b, the stator structure in MPMSM is segmented and, therefore, the attachment of the modules to the stator body can provide the design with additional manufacturing and assemblies tolerances (uncertainties) when compared with conventional PMSMs (Figure 1a). Recent studies have approached the analysis of some of these uncertainties, giving insight into the effect of design parameters and dimensional tolerances on the machine performance [15; 17; 18]. Although these studies are relevant for describing the impact of dimensional tolerances on the performance of MPMSMs and provide guidelines for devising more robust designs, there is a critical uncovered aspect that compromises the reliability and continuous operation of these machines: stator-rotor misalignment. Stator-rotor misalignment, which can be classified into static eccentricity or dynamic eccentricity depending on the dynamics of the misalignment [24; 25], wears down the bearings since it generates vibration and pulsing forces on their structure [26; 27] and can truncate the fault-tolerance capability of electrical machines. In addition, eccentricity affects the performance of several topologies in terms of the generation of radial forces in the rotor structure [27; 28; 29], cogging and ripple torque increase [24; 30], input current harmonic distortion when the machine is fed with inverters [31], and back-emf unbalance [30]. Studies on eccentricity effects are particularly relevant in PM machines, as the magnets on the rotor can generate significantly high radial forces on the stator structure and the bearings [24], which can trigger a major fault. The impact of eccentricity on PMSMs with non-segmented stators has been covered in [25; 26; 27; 29; 30; 31], focusing on quantifying and analyzing the effects on the electromagnetic performance of the machine.