Dual Mode Dual Stator Wound Rotor Synchronous Machine for Variable Speed Applications

Electric vehicles and hybrid electric vehicles are being developed as a means to extenuate the environmental concerns. Permanent magnet (PM) machines have been used for such applications due to their high torque density, robust structure and no need for an external excitation system. However, the limited supply and increasing price of PM material create a need to search the alternative solutions such as the brushless wound rotor synchronous machines (BL-WRSM). Several brushless topologies for WRSMs have been presented in [1- 3]. In [1] and [2], the brushless operation of WRSM is achieved by utilizing sub-harmonic and third harmonic components of stator MMF, respectively. In [3], the sub-harmonic component of stator MMF is generated by dividing the stator winding into two sets of series connected windings, which are then supplied through a single inverter. In the brushless topologies, the stator current is the only source of excitation and the field current is induced from the harmonic component of MMF. When the machine operates below the rated speed, the induction process slows down and the magnitude of the field current is gradually decreased with the decrease in the speed of the machine. Therefore, the torque in the constant torque region cannot be maintained constant by the BL-WRSM. However, at or above the rated speed these machines work properly. In this paper, a dual mode dual stator wound rotor synchronous machine (DMDS-WRSM) for variable speed applications is proposed. Through the dual mode (DM) machine operation, the constant torque and the constant power are achieved in the constant torque and constant power region, respectively. However, the dual stator design has been chosen to improve the torque density of the machine as compared to the torque density of the single stator BL-WRSM presented in [3]. A 2-D finite element analysis is performed to validate the proposed DMDS-WRSM.