A Novel Counter-Rotating AFPM Machine Based on Magnetic-Field Modulation for Underwater Propulsion System

The underwater propulsion system (UPS) with two counter-rotating propellers is very popular now. In tradition, it needs two electric machines or additional gears, which greatly increases the volume and weight of the system. Therefore, a novel counter-rotating axial-flux permanent magnet (AFPM) machine based on magnetic-field modulation (MFM) for the UPS is proposed. It contains a more pole rotor and a less pole rotor on two sides. The MFM is achieved through the split teeth on the stator. Based on the MFM, the two rotors can rotate in opposite directions. The principle of MFM and the relationships of rotary speeds between two rotors are analyzed. Furthermore, the effects of split tooth shape and dimensions on the performances of the proposed machine are also evaluated. The triangular skew fan-shaped split teeth are adopted in the counter-rotating AFPM machine. Finally, the prototype is manufactured and an experiment is conducted to validate the performance. The results show the consistency of analysis and experiment.