Reduction of Torque Ripple and Vibration of Permanent Magnet Synchronous Machines with Sinusoidal Cavities

In the design process of electrical machines for traction applications, a strong focus is placed on noise, vibration and harshness (NVH) to improve the customer’ s driving experience. Parasitic effects like torque pulsations and acoustic vibration in interior permanent-magnet synchronous machines (IPMSM) are usually reduced by step-skewing of the rotor. However, this approach results in a lower output torque due to the reduction in fundamental harmonic flux linkage between the rotor field and the stator winding. Additionally, the cost of the machine is increased by the more complex and time-consuming manufacturing process.In this paper, the influence of sinusoidal cavities on the performance of V-shaped buried-magnet topologies is investigated. This modification of the rotor influences the flux density distribution in the air gap and thus the amplitudes of the spatial harmonics. Since torque pulsations and the radial forces are directly correlated to the air-gap field, the acoustic behavior will be affected. As the cavities can be integrated into the punching process for the rotor laminations, this offers a cost-efficient approach for reducing the unwanted parasitic effects in the machine. To identify a favorable design, a parameter study is carried out and the air-gap flux density distribution of the rotor field is evaluated. The torque behavior and the acoustic noise emissions of the machine with sinusoidal cavities are compared to the unskewed and the step-skewed reference machines.