cogging torque reduction of a bldc motor used for evaporative water coolers

In recent years, permanent magnet brushless dc (bldc) machines have attracted significant attention in evaporative water cooler applications due to their high efficiency, high torque density, and wide range of speed control capability. however, their relatively large cogging torque has been recognized as a notable challenge for such applications. this paper, therefore, aims to introduce an alternative approach to address the cogging torque issue without compromising other motor characteristics. in this regard, by developing two-dimensional finite-element (2d-fe) models, four schemes are analysed, separately, including stator slot skewing, rotor step-skewing, rotor pole-notching, and non-uniform airgap. then, by utilizing a multi-objective problem, an optimum design is achieved, demonstrating superior performance in terms of minimum cogging torque, and maximum back-emf and efficiency.