| With the improvement of the performance of permanent magnet materials and the development of permanent magnet motor manufacturing technology, line-start permanent magnet synchronous motors (LSPMSM) are widely used in oil field, and etc. Compared with electrically excited synchronous motor and induction motor, LSPMSM has advantages of high efficiency and power factor, high energy density, etc. However, due to the interaction between the permanent magnet and slotted armature lamination, there exists cogging torque which may cause noise and vibration. Cogging torque must be seriously considered and reduced.Compared with the analysis of cogging torque in surface-mounted permanent magnet motor (SMPMM), due to the existence of stator slot and rotor slot, the changing of effective air-gap length is very complex, which increases the complexity of the analysis of the cogging torque. In this paper, a novel method is proposed to analyze the cogging torque for LSPMSM. According to the structural characteristics of LSPMSM, each tooth on the rotor is taken as a permanent magnet attached to the rotor surface, similar to permanent magnet attached to the rotor surface in SMPMM. The effective air-gap length is only affected by the stator tooth-slot, thus the analysis of cogging torque in LSPMSM is simplified.At first, based on energy method and Fourier expansions, the expression of cogging torque is deduced. Obtained by analyzing coefficients of the Fourier decomposition of the air gap flux density which play an important role to the cogging torque, several methods are obtained, including changing the rotor tooth width, different rotor tooth widths, different rotor slot widths, changing the shape of the rotor tooth, changing the stator slot width, different stator slot widths and auxiliary slot in the top of stator teeth, etc. For each method, the method for determining parameters is deduced, and the effectiveness of the above methods are proved by the Ansoft MAXWELL finite element analysis software. |
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