Optimization of Line Start Permanent Magnet Synchronous Motor for Magnet Cost Reduction

University essay from KTH/Elektrisk energiomvandling

Abstract:

In this thesis different methods of optimizing line start permanent magnet motor (LSPM) for magnet cost reduction is studied. Influence of different parameters has been studied by simulating magneto-static and transient FEM models of the machine. Finally a motor design of a LSPM with high rotor saliency has been proposed.

The first method investigated is the use of flux barriers in LSPM and its effect on the magnetic flux leakage. The flux barriers reduce the flux leakage and hence help in reducing magnet volume. The second method studied is the use of two different grades of magnets. Using low price magnets help in reducing the total magnet cost without reducing the air gap flux density. The reduction in NdFeB magnet volume is not substantial by using both the methods mentioned above.

The third method investigated is increasing the saliency of the rotor by introducing flux barriers and reducing the corresponding magnet volume. Both the magneto static and transient models are used to study the effect of different parameters of the motor. The placement and volume of magnet plays a critical role in motor performance. At first, the developed reluctance torque of the motor is maximized by doing parametric study and then magnets are placed in slots to achieve the required efficiency and power factor. The motor is simulated with NdFeB magnets and with Ferrite magnets. It has been found that using high saliency LSPM motor the NdFeB magnet volume can be reduced significantly. It is also shown that the same performance of motor (as compared to the motor with NdFeB magnets) can be achieved by using Ferrite magnets. The volume of Ferrite magnet required will be larger but still cost-wise using Ferrite is an attractive choice. Therefore, a design of motor is proposed using both NdFeB magnets and Ferrite magnets. Finally, the performance of proposed LSPM motor with high saliency is compared with that of an induction motor.

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