A Novel Coupling Slippage Control Algorithm to Improve Post-LVRT Performance of High Power Wind Turbines

The increased integration of renewable resources pushes the grid to a dynamic stability limit, and system operators are mandating stringent grid codes mainly related to voltage ride-through events. The LVRT performance and reactive power support, as per the stringent grid codes, exert high mechanical stresses in the wind turbine (WT) drivetrain, creating the chances of the failure of sensitive components especially gear teeth and bearings. The WT drivetrains are inherently protected against over-torques by using a mechanical slip coupling device, which causes disengagement of the drivetrain when the torsional stresses exceed a threshold value. At times, the slip coupling operation may not result in re-engagement, causing large mechanical imbalance forces acting on WTs that lead to turbine shutdown. This paper proposes a novel coupling slippage control algorithm based on estimated shaft torque and generator power set-point to increase the possibility of re-engagement without actually shutting down the WT. The estimated shaft torque-based coupling slip detection method is proposed to detect coupling slippages more quickly and accurately than conventional methods. To study the internal dynamics behaviour of WTs during the coupling slippage events, a 3D model of 5 MW WT was developed using SIMPACK and is integrated with the electrical system model in MATLAB Simulink. The proposed control algorithm was verified using a co-simulation of MATLAB Simulink and SIMPACK for a deep dip LVRT test case scenario.