Control Strategy to Mitigate the Shaft Torsional Oscillation of PMSG-based WECS Using <i>H</i>_∞ Controller

Abstract

One of the challenges facing modern large-scale wind turbines stems from the shaft which has a finite stiffness, leading to shaft torsional oscillation which creates fatigue fractures and overload in the shaft system causing unexpected downtime of the wind turbines (WTs). In this study, the shaft torsional oscillation is investigated using a two-mass model of the shaft system. The permanent magnet synchronous generator is operated as a suppressor to mitigate the shaft torsional oscillation by implementing an 𝐻 ∞ controller in the speed control loop, thereby enabling the closedloop control system to reduce the effect of shaft torsional oscillation. Another challenge lies in inability to directly measure the shaft torsional torque. Thus, the shaft torsional torque estimate is obtained by the 𝐻 ∞ observer. Both observer and controller are designed using the linear matrix inequality method. The simulation results were obtained using Matlab/Simulink @ to analyze the effectiveness of the proposed control under highly oscillated wind. Based on the results, the shaft torsional motion was mitigated by the suggested control technique as compared to the standard control method. The estimate result proved that the 𝐻 ∞ observer was effective under various conditions that affect the performance of the observer.