Characteristics of an axial-flux permanent magnet synchronous machine with contra-rotating rotors under unbalanced load condition from 3-D finite element analysis

During recent years, the axial-flus PMSM with contra-rotating rotors has become a hot topic in academic research due to its high efficiency and simple structure. However, its back-EMF may be distorted under the condition of different angular positions. This paper investigates characteristics of the novel motor used for contra-propeller driving. Considering the torque ripple and current oscillation under unbalanced load condition, this paper analyzes the distorted back-EMF of the machine when its two rotors get different angular positions during rotating. The analysis results are validated by transient-magnetic 3-D FEA method, which the 3-D FEA software is used to model this motor and transient simulations are carried out to obtain its magnetic characteristic and main performances. A main focus is put on the back-EMF characteristic with different angular positions between the two rotors. Furthermore, the characteristic of torque production under unbalanced load is investigated. Finally, a prototype motor is fabricated to validate the analyses of this paper.