Slot opening optimization of surface mounted permanent magnet motor for cogging torque reduction

In this paper, slot opening skew method is used for cogging torque reduction. A three layer stator model is considered for a six-pole PM-BLDC motor (a PM-BLDC motor with 18-slots, six-poles and length of 5 cm) and then a 2D dual model is extracted for this 3D slot opening skew model. The angular shifts of slot opening position in the first and third layers than middle layer are considered as optimization parameters. Slot opening shape is optimized by using different optimization algorithms, such as, the response surface methodology (RSM), the genetic algorithm (GA) and the particle swarm optimization (PSO). In order to using of GA and PSO, the analytical relationship is derived for the air–gap permeance function. The optimization results of these algorithms are being consistent with each other and are verified with FEA results. The results show the significant reduction of cogging torque about 77%.

► The slot opening shift method is an efficient method for cogging torque reduction.
► Using slot opening skew method, the trapezoidal waveform of back-emf is maintained.
► Using the conventional slot skewing, the wave shape of back-emf is sinusoidal.
► The novelty of paper is using of air–gap permeance harmonics as objective function.
► Other novelty of this paper is using the different optimization algorithms.