Radial force characteristics of a switched reluctance machine

The operation of a switched reluctance machine with eccentric rotor positions creates asymmetrical airgap flux distributions and results in unbalanced magnetic pull. This paper comprehensively investigates the static and dynamic radial force characteristics of an 18/12 switched reluctance machine with unbalanced operation. A powerful magnetic equivalent circuit (MEC) modelling approach is developed and allow fast and accurate force predictions with arbitrary excitation and position. The model calculates the instantaneous radial and tangential forces on the individual poles as well as the net forces on the rotor. The method is validated with finite element analysis (FEA) and against experimental results from a 12/8 machine. Static radial force characteristics are first developed. The MEC is then coupled with a time stepping algorithm to calculate the simultaneously varying electrical, mechanical, and magnetic variables for dynamic operation of the complete SR motor drive. Dynamic radial force behavior is examined, where parallel connected windings are found to naturally and significantly reduce the unbalanced magnetic pull. Variations of radial force with torque-speed operating point are also examined