Analytical Solution of the Magnetic Field and EMF Calculation in Ironless BLDC Motor

The ironless brushless DC (BLDC) motors are widely used for flywheel due to their light mass, high efficiency, and high inertia-to-mass ratio. In this paper, a 2-D analytical solution for predicting the magnetic field distribution in an ironless BLDC motor is presented and compared with the 2-D finite-element method (FEM). The results of the proposed 2-D analytical method and the 2-D FEM are in good agreement. It is also found that the intensity and direction of the magnetic field change largely in the coil region, which makes the electromotive force (EMF) of strands in one coil package different from one another. Hence, three different models to calculate the EMF of ironless BLDC motor are proposed and compared. Meanwhile, both the axial end effect and the influence of end winding on EMF are considered, and then, a correction factor is proposed for the ironless BLDC motor. The effectiveness of the proposed method is validated by the experimental results. Due to its accuracy and computational speed, the method can be used in the design and optimization of ironless BLDC motors.