Analysis of vibration induced by cogging torque in permanent-magnet synchronous motors

Noise and vibration of electrical machines are a major concern for applications where comfort is a significant aspect. There are several faults that may arise in machines increasing noise and vibration. Cogging is one of the main faults in Permanent Magnet Synchronous Machines (PMSMs). Tools for the diagnosis of cogging are needed to detect the machines that do not fulfil the quality requirements. The usual methods found in bibliography to assess cogging are Motor Current Signature Analysis (MCSA) or directly measuring it by means of a torque sensor. This paper studies the feasibility of the alternative and unpublished method of vibration signals measured with accelerometers to evaluate cogging. In this paper a machine is designed and manufactured, in order to measure the effect of cogging in the vibration of the machine. The tested machine allows to apply several cogging levels, and the vibrations and the torque are measured with the machine running at several rotational speeds. Especially at lower rotational speeds, the effect of the cogging is clearly observed in the spectra of the torque. However, the spectra of the vibration signals do not show the effect of cogging torque, since at the cogging frequency the amplitudes do not correspond to the cogging levels.