Armature Reaction Field and Inductance Calculation of Ironless BLDC Motor

The analysis of armature reaction field and winding inductance is extremely important for the design and control of electromagnetic motors. In this paper, a more accurate analytical model to predict the armature reaction field of an ironless brushless dc motor having either non-overlapping winding or overlapping winding is presented. First, for a non-overlapping winding analytical model, the field domain is divided into three subdomains, and for an overlapping winding analytical model, the field domain is divided into four subdomains. Second, the armature current model is established, and the field solution is obtained by solving Maxwell's equations through the variable separation method and the use of adequate boundary and interface conditions. Third, the magnetic flied distribution in different subdomains calculated by the analytical method is compared with that calculated by the finite-element method (FEM). Last, the winding inductance is investigated as it is relatively small for an ironless motor, which introduces serious current/torque ripple. The accurate calculation of inductance is important for facilitating dynamic motion control. The results obtained by the analytical method and the FEM are compared and are in good agreement. A research prototype is developed, and experiments are carried out to verify the analytical results.