I. Introduction
Fractional-slot concentrated-windings (FSCW) permanent magnet (PM) machines have been widely applied in transportation systems attributed to the advantages of high torque density and low cogging torque [1]–[4]. However, poor vibration performance is one of the typical demerits of FSCW PM machines [5], [6]. The eminent torque performance and unsatisfactory vibration response constitute the inherent contradiction issue of the FSCW PM machines.