Mitigation of magnetic flux saturation in dual-excitation flux switching motor

Abstract

Development of dual-excitation flux switching machines (DEFSMs) in which the combination of permanent magnet (PM) and DC field-excitation coil (FEC) as their main flux sources has been carried out over many years. This is due to their definite advantage of variable flux capabilities with high potential to gain much higher torque and power densities, as well as higher efficiency over conventional PM machines [1-3]. Early example of 6S-4P DEFSM where all active parts of armature coil, FEC and PM are stacked in inner, middle and outer stator respectively, has been designed [4-5]. Since, all flux sources are arranged in three layers, the machine inherits overlap armature and FEC windings which increase the coil end and copper loss. Besides, several 12S-10P DEFSMs have been developed based on the topology of purely PM excited PM machine such as (i) the PM dimension is reduced to save space for the introduced FECs, whilst both stator and rotor laminations are unchanged [6] (ii) the PM is partially replaced by several FEC formations [7-8] and (iii) the middle teeth of E-Core PMFSM is replaced with FEC to form E-Core DEFSM [9]. Although they have no overlap armature coil and FEC, the flux adjusting capability is fairly limited due to low PM permeability resulting from series PM and FEC excitation, while the torque capability is significantly reduced due to less PM volume. In addition, the foregoing DEFSMs also consist of PM along the stator radial, thus the PM flux certainly leaks around the outer stator and a perfect circle shape is hard to be fabricated due to segmented stator core. Contrariwise, a 12S-10P DEFSM in which the FEC is incorporated at outer extremity of the stator has been introduced with advantages of no flux leakage outside the stator and single piece stator for ease of fabrication [10-11]. However, the designed machine has some limitations of torque production in high current density condition due to insufficient width between active parts resulting in magnetic flux saturation and negative torque production. In this paper magnetic flux saturation of 12S-10P DEFSM is analyzed and mitigation technique using deterministic optimization approach is proposed to increase the torque production.