Vibration analysis of a permanent magnet synchronous motor by a pole/slot combination

A sixteen-pole eighteen-slot (16p/18s) permanent magnet synchronous motor (PMSM) developed in Korea Electrotechnology Research Institute (KERI) for a vertical articulated robot is chosen as a reference model, and other two pole/slot combinations (20p/18s, 20p/24s) are together compared in terms of electrical and mechanical performance. Radial force density varying in time and space is decomposed through Fast Fourier Transform (FFT), and vibration is calculated from the harmonics of radial force. The vibration of 20p/24s is best due to its mode of 4 among the three pole/slot combinations. Additionally, the variation of radial force density with respect to torque is compared between 16p/18s and 20p/18s. Despite the same number of slots in both motors, the slope of 20p/18s is greater than that of 16p/18s in radial force density due to the different number of poles. As a result, the vibration of 20p/18s is worse than that of 16p/18s.