This paper investigates reduction of cogging torque and acoustic noise in permanent magnet motors with larger stator slot opening. Using energy method with Fourier series expansion, cogging torque is analytically determined with airgap MMF function and airgap permeance function. It shows that there exist several tooth widths which minimize the cogging torque. It also proposes a teeth pairing with two different types of tooth width which can effectively reduce the cogging torque and thus the acoustic noise. Experimental results show that the proposed teeth pairing reduces the cogging torque by 85% and the acoustic noise by 3.1 dB.
Vibration of a crankshaft-journal bearing system driven by an electric motor is a coupled phenomenon between hydrodynamic characteristics and magnetic origins through the motor air gap. With the advent of new high-energy magnets together with variable speed motor applications, magnetic sources of vibration are becoming more serious. This article investigates the transient whirl responses of a rotor system with purely hydrodynamic origins and compares it with that of magnetically coupled origins. Results show that magnetically coupled sources significantly affect the vibration of the rotor-motor system.
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