Study on a composite differential magnetic gear integrated dual-stator flux-modulated permanent magnet brushless machine for offshore wind energy production

The conventional single-stator wind turbine typically suffers from low power and torque densities, reduced efficiency, and limited reliability. To address these issues, a semi-direct-drive offshore wind turbine is proposed, which utilizes a composite differential magnetic gear (CDMG) axially integrated with a dual-stator flux-modulated permanent magnet brushless (DSFMPMB) machine, referred to as the CDMG-DSFMPMB system. The key novelty lies in the axial integration of the CDMG with a dual-stator flux-modulation structure. This configuration enhances the magnetic field modulation capability and enables effective electromagnetic coupling between low-speed and high-speed components. With the modulation module, the armature magnetic field in the stator can be modulated at high frequency, allowing effective matching with the rotor permanent magnet field under low-speed operation. By combining the flux-modulation principle with a dual-stator configuration, the proposed system achieves improved wind energy conversion efficiency and higher power density. In addition, the integration of the CDMG enables low-speed operation with high torque output and enhanced torque density, making it particularly suitable for offshore wind energy applications. This paper presents the topology and operating principles of the proposed CDMG-DSFMPMB system. The electromagnetic characteristics of the machine and the torque performance of the CDMG are evaluated using the finite element method (FEM). The results show that the back electromotive force (EMF) amplitudes of the inner and outer armatures increase by 114% and 81.39%, respectively. Furthermore, the torque density of the CDMG reaches 118.01 kNm/m 3 , demonstrating the effectiveness of the proposed design.