Stator skew optimization for low-wind-speed starting and ripple mitigation in portable micro vertical-axis wind turbine

To resolve low-wind-speed starting difficulties and mechanical vibrations in portable vertical-axis wind turbines (VAWTs) caused by excessive cogging torque of the generator, this paper proposes a brushless outer-rotor permanent magnet generator featuring a 1.36° stator skew. Evaluated via finite-element analysis (FEA) and aerodynamic–mechanical–electrical co-simulation, the skew reduces the peak-to-peak no-load torque ripple from 10.679 mN·m to 0.101 mN·m (99.05%) while decreasing the peak phase back-EMF only from 14.29 V to 14.24 V and the mean phase THD from 25.47% to 24.87%. Under a constant 1.5 m/s low-wind-speed quasi-no-load condition, the skewed-slot design mitigates transient torque ripples and stabilizes the DC output voltage at approximately 7 V. Upon connecting a 20 Ω load, torque oscillations are reduced while the output remains approximately 0.98 V. These results support the effectiveness of stator skewing for improving low-speed starting and mechanical smoothness in portable micro wind power systems.