Shape optimization of closed slot type permanent magnet motors for cogging torque reduction using evolution strategy

The analysis of a permanent magnet-type AC servo motor with both a closed slot and a ring shape magnet is performed by using the finite element method (FEM). The saturation of the bridge-part connecting two slot teeth is considered for nonlinear analysis. The optimal design of the stator is presented for minimizing cogging torque. The torques, i.e. cogging and rated torques, are expressed in terms of vector potential computed by directly applying the Maxwell stress tensor formula. The minimization of cogging torque of sample model is achieved by using the (1+1) evolution strategy (ES) and the rated torque must be more than the specific value.