Design of Notches on Rotor Surface to Minimize Cogging Torque in Dual-Layered IPMSM by Optimizing Squared Gap Flux Density Waveform

This paper proposes a method to design the notches on the rotor surface to reduce the cogging torque of the double-layered interior permanent magnet synchronous motors (IPMSMs). The proposed method designs the notches mainly based on theoretical equations and can be applied to general double-layered IPMSMs regardless of the magnet arrangement. First, the waveform of squared gap flux density $(B_{g^{2}})$ of an initial model is approximated by a two-step trapezoidal waveform. Based on this approximate waveform, the pulsating component of the waveform of $B_{g^{2}}$ is formulated when the notches are provided on the rotor surface. In addition, the waveform of $B_{g^{2}}$, in which the main pulsating components of the cogging torque can be zero, is derived. The position and width of the notches were determined based on the derived waveform, and only the notch depth was adjusted by FEM analysis. As a result, the cogging torque of the model with the optimized notches was reduced by 83%.