MTPA Characteristic Analysis based on Load Angle for Dual-Rotor PM Synchronous Motor

The dual-rotor permanent magnet synchronous motor (DR-PMSM) was investigated to reduce the mechanical losses and the maintenance of mechanical speed reducers in railway vehicle driving systems. The DR-PMSM consists of a non-contact magnetic gear with two rotors, permanent magnet (PM) rings, and three-phase stator windings. The torque of the DR-PMSM depends on the load angle between the inner and outer rotors, as well as the field flux and stator current. The high efficiency operation of the DR-PMSM can be achieved through vector control, similar to that of a conventional three-phase permanent magnet synchronous motor. Unlike the conventional three-phase PMSM, the dq current for highly efficient operation of the DR-PMSM exists in the first quadrant of the dq-axis current plane. The torque of the DR-PMSM consists of the magnetic, reluctance, and modulation flux torques. This study analyzes the operating point of the dq current for MTPA operation in DR-PMSMs. The characteristics of MTPA operation are verified through MATLAB/Simulink simulations and experiments using a 1 kW DR-PMSM.