Analytical modal for round square PMDC motor

According to the study of traditional cylindrical PM motor, it is generally acknowledged that the electromagnetic radial force is the root cause of electromagnetic vibration and noise, However, for round square PM motor, the tangential force is the main cause of electromagnetic vibration and noise besides radial force, for its geometry structure and electromagnetic characteristic. This paper deduces piecewise function regarding the stator electromagnetic force, based on round square motor circumferential piecewise electromagnetic model. Set up round square motor radial and tangential force geometric model. Based on the geometric model, round square motor electromagnetic vibration and acoustic radiation can be expressed in formula, combine the modal analysis result, indicating that radial force is the main driving source of first order mode for round square motor, and tangential force is the main one of the second order mode. The study provides theoretical basis to round square PM motor noise analysis, and presents directive significance for root causes, reduction and restraint of round square motor vibration and noise.