Analysis And Suppression Of Unilateral Magnetic Force In Permanent Magnet Synchronous Machine With Fractional-slot Winding

Under the dual pressures of the energy shortage and the environment pollution,the electric vehicle will be the substitute for the traditional internal-combustion enginevehicle for its advantages, such as high efficiency of the energy sources usage, lowemission of the pollution and so on. Among overall vehicle dynamical characteristic,motor drive system is very important. And the permanent magnet synchronous motor（PMSM）is an ideal choice because it’s high efficiency, high torque density, lowvibration and noise and other excellent advantages.Permanent magnet synchronous motors with fractional slot winding has hugeadvantages not only in motor manufacturing process but also in the motor overallperformance, especially in small and medium power applications, the fractional slotwinding structure has been widely used. When the permanent magnet synchronousmotor is running, the stator mmf interacts with permanent magnet mmf to generateelectromagnetic force. The electromagnetic torque is generated by the tangentialcomponent of the electromagnetic force, but the radial component will cause vibrationand noise in the motor. And fractional slot winding structure will increase theimbalance of motor radial magnetic force in some way. So the analysis andsuppression of unbalanced magnetic force in permanent magnet synchronous motorwith fractional slot winding has important practical significances for enhancing theoverall performance of electric vehicle drive motor.It describes the advantages of permanent magnet synchronous motor design withfractional slot winding, makes8-pole9-slot and10-pole9slot motor structures whichare frequently used in small-medium power applications to explain theelectromagnetic reasons and the mechanical reasons of the formation of theunbalanced magnetic force, as well as the motor overall performance and the effectsto vibration and noise in particular. The numerical method of unbalanced magneticforce for permanent magnet synchronous motor is deduced, and the finite elementsimulation is made to analysis and comparison of the specific cases. The three mainelectromagnetic factors which cause the unbalanced magnetic force of permanentmagnet synchronous motor with fractional slot winding is summed. For each case,three suppression measures are proposed respectively, which are optimizing the coordination number of poles and slots, optimizing the armature current andoptimizing the air-gap flux density harmonics. The brief theoretical analysis and finiteelement simulation is made for each measure. Facts have proved that the threemethods mentioned above can restrain unbalanced magnetic force of permanentmagnet synchronous motor with fractional slot winding effectively, reduce thevibration and noise of the motor, and improve motor overall performance in a largeextent.