Comparative Analysis of Electromagnetic Vibration and Torque Ripple of Multi-Unit PMSMs Under Normal and Fault Operation

In order to study the electromagnetic vibration and torque ripple of multi-unit permanent magnet synchronous motors (PMSMs), an analytical model of flux density under multi-unit operation was established. The spatiotemporal characteristics of 2-D air-gap flux density, electromagnetic force, and electromagnetic torque were explored, and the characteristics of electromagnetic force and vibration response under unit-missing operation were analyzed. First, the flux density analytical models under the operation of one unit and k unit motors were established, and the spatiotemporal distribution law of electromagnetic force and electromagnetic torque was analyzed. Then, the vibration response under unit-missing operation was theoretically derived and analyzed; finally, the prototype was simulated and experimentally verified. With k unit motors, the electromagnetic force and torque components exhibit harmonics with angular frequency $2\pi (2hf_{e})$ and $2\pi (6hf_{e})$ , $h\in \mathbb {N}$ , respectively ( $f_{e}$ supply line frequency). The unbalanced electromagnetic pull resulting from the lack of a single unit introduces additional force harmonics, whose frequencies differ from those in balanced operation by multiples of the rotation frequency $f_{r}=f_{e}/p$ (p: pole pairs) that, however, are not generally multiples of $f_{e}$ .