Magnetic field analysis of double excited synchronous motor using numerical conformal mapping

Double Excited (or Hybrid Excited) Synchronous Motors (DESM or HESM) has gained great interest as they have the ability to control the air-gap field, and consequently the electrical drive speed due to the auxiliary excitation winding. To obtain the magnetic field distribution in the air gap many techniques are used. The Schwarz-Christoffel (SC) mapping allows the mapping of the slotted structure of the machine to a simple geometry domain for which analytic solution is known. In this paper, we apply a SC conformal mapping method to a DESM using the SC Toolbox of MATLAB to analyze magnetic fields originating from Permanent Magnet (PM), auxiliary excitation winding and armature winding currents in stator slots. This field solution is used to calculate cogging torque and electromagnetic torque using Maxwell stress tensor and to calculate back-EMF. Analytical results are compared to Finite Element Analysis (FEA) to verify the accuracy of developed model.