Analysis of drive-train resonance and torque ripple smoothing of a 50kW vertical axis wind turbine

Two-blade vertical axis wind turbines (VAWTs) are well-known for their pronounced torque ripples. Left unattended, the torque ripples not only cause significant adverse mechanical effects on the drive train components, but also worsen the quality of the output power of the wind generator and the associated power converters. Moreover, the resulted power fluctuations will propagate through the distribution and may induce further inter-area oscillations when a number of turbines are aggregated and connected to the distribution network. This paper presents the analysis of the resonance phenomenon and torque ripple produced by the drive train of a 50 kW VAWT generating unit designed and built by Cranfield University. The analysis is based on a mathematical model derived for the DriveTrain of this unit. Based on the analysis, optimised drive shaft dimensions can be determined for safe operation without the risk of shaft resonance, and an electromagnetic torque ripple smoother is also proposed.