Cogging Torque Reduction in Line Start Permanent Magnet Synchronous Motor

Abstract

-Cogging torque has a negative impact on the operation of permanent magnet machines by increasing torque ripple, speed ripple, acoustic noise and vibration. In this paper Magnet Shifting Method has been used as a tool to reduce the cogging torque in inset Line Start Permanent Magnet Synchronous Motor (LSPMSM). It has been shown that Magnet Shifting Method can effectively eliminate several lower-order harmonics of cogging torque. In order to implement the method, first the expression of cogging torque is studied based on the Fourier analysis. An analytical expression is then introduced based on Permanent Magnet Shifting to reduce cogging torque of LSPMS motors. The method is applied to some existing machine designs and their performances are obtained using Finite Element Analysis (FEA). The effect of magnet shifting on pole mmf (magneto motive force) distribution in air gap is discussed. The side effects of magnet shifting on back-EMF, core losses and torque profile distortion are taken into account in this investigation. Finally the experimental results on two prototypes 24 slot 4 pole inset LSPMS motors have been used to validate the theoretical analysis.

Archives of Electrical Engineering

“…During the starting process, the flux of the permanent magnets generates a braking torque which reduces the resultant asynchronous torque produced by the cage winding, this phenomenon is especially observable at the low range of rotational speeds of the rotor. One of the ways to mitigate this problem is increasing the resistance of the cage, whereby the breakdown slip shifts towards lower rotor speeds and, consequently, the starting torque increases [6,7]. However, it should be noted that lowering the value of the breakdown slip will reduce also the "pull in" torque and can lead to a failure of the synchronization process of the motor for high inertia loads [8].…”

Parametric Analysis for Performance Optimization of Line-Start Synchronous Motor with Interior Asymmetric Permanent Magnet Array Rotor Topology

“…In other analyzed operating points during motor acceleration, the demagnetization of magnets should not occur. The numerical model allows magnetic flux density distribution to be calculated in the motor cross-section by the aid of Finite Elements Method (FEM) thus allowing parts of the magnetic core with high flux density to be detected [22][23][24]. Another aspect of analysis of the models is the transient characteristics where the motor behavior in transient regimes such as start-up can be analyzed [25,26].…”

An Analytical Method for Determining Flux Density in Surface-Mounted Permanent Magnet Machines with Unequal Magnetic Poles

“…Moreover, the electromagnetic characteristics of the motor can be changed by altering the configuration scheme of the PM. This is an effective way of improving the electromagnetic properties of the motor [16]. Converting the configuration scheme of the PM includes mounting the PMs with different polar-arc coefficients or the PMs with different remanences.…”