Effects of Eccentricity on the Back EMF of Multimodule Permanent Magnet Synchronous Machine for In-Wheel Traction Applications

Eccentricity is common in electrical machines due to manufacturing error and assembly deviation, which can distort the back electromotive force (EMF) and further affect the reliability of electrical machines. For multimodule electrical machines, the effect of eccentricity on the back EMF varies with regard to different parallel combinations of submodule windings. In this article, an analytical model based on the air-gap field modulation (AFM) theory is proposed to investigate the effect of eccentricity on the back EMF of a four-module in-wheel electrical machine, where four available combinations are considered: each submodule in separate operation (1000), two adjacent submodules in identical phase-parallel operation (1100), two diagonal submodules in identical phase-parallel operation (1010), and four submodules in identical phase-parallel operation (1111). The proposed analytical model demonstrates that the 1010 and 1111 combination patterns can effectively mitigate the negative effect of eccentricity on the back EMF. After simulation, the aforementioned conclusions are further accredited by experiments conducted on a 72-slot 80-pole four-module outer rotor surface-mounted permanent magnet synchronous machine (SPMSM).