Fast prediction of unbalanced magnetic pull in PM machines

In this work, a model is proposed for the computation of unbalanced magnetic pull (UMP) in PM machines. This model is suitable for use in dynamic simulations. However, the aim of this research is not dynamic modeling of the PM machines. The main idea is to provide a fast model to be integrated into the dynamic models of PM machines. To reduce the required computational burden, the UMP of PM machines is expressed as a second-order algebraic vector function of the stator currents. The function parameters are estimated by post-processing of the results of some magneto-static simulations. These parameters are functions of the machine geometrical data and the rotor position. The role of these parameters in the computation of the machine UMP is the same as the role of the machine inductances in computation of the electromagnetic torque. To investigate the capability of the developed model, the UMP of a concentric fractional-slot surface PM machine with diametrically asymmetric stator windings and the UMP of an eccentric PM-inset machine are predicted. The obtained results are compared in terms of the consumed time and the accuracy by means of finite element analysis.