Original Paper

Electrical Engineering

, Volume 95, Issue 3, pp 209-219

First online:

Open Access This content is freely available online to anyone, anywhere at any time.

Investigation on a choice of stator slot skew angle in brushless PM machines

  • M. JagielaAffiliated withDepartment of Electrical Engineering, Automatic Control and Computer Science, Opole University of Technology Email author 
  • , E. A. MendrelaAffiliated withElectrical and Computer Engineering Department, Louisiana State University
  • , P. GottipatiAffiliated withElectrical and Computer Engineering Department, Louisiana State University


The paper investigates the effects of stator slot skewing in a permanent magnet brushless DC motor. A simple analytic formula for calculation of the best angle of stack skew, which leads to nearly total reduction of the cogging torque, is developed. The skew angle obtained from this formula is different to that used by the designers of PM brushless motors. The analysis is carried out for a fractional horsepower brushless permanent magnet motor with the surface-mounted magnets using a time-stepping, multi mesh-slice finite element model, to assess the impact of this change. The steady-state characteristics and core losses are analyzed quantitatively using the elaborated numerical model. It is shown that smaller skew angles obtained from the formula lead to noticeable rise in motor overall efficiency and decrease of the core loss. The possibility of accomplishment of the desired effect of skew in a real machine is also a subject of discussion.


Permanent magnet brushless DC motors Slot skew Core loss Electromagnetic torque Finite element analysis