A research on the radial unbalanced force in the unsymmetrical brushless PM motors

The brushless PM motors with concentrated windings have some common advantages such as the reduction of copper volume in the end-windings and low cost. Among these motors, some brushless PM motors with special unsymmetrical structures have particular advantages including high winding coefficient and low cogging torque. Those common advantages and particular advantages make the unsymmetrical brushless PM motors with concentrated windings suitable for drive system with high performance demand. However, there is a radial unbalanced force in this kind of motor due to their unsymmetrical structures. In this paper, the radial unbalanced force is studied using FEM through two motor models which have unsymmetrical structures. It can be seen from the simulation results that this unbalanced force exists under both sinusoidal and trapezoidal drive current. This force may cause acoustic noise in operation. Corresponding considerations should be given when applying this type of motors.