The Effect of Blade Deflections on the Torsional Dynamic of a Wind Turbine

Abstract

The dynamic behavior of a wind turbine comprises three major parts: the external torque produced by the wind, the mechanical elements and the grid. For the aerodynamic response, there is three type of models: constant aerodynamic torque for Type I and Type IV turbines, a pseudo aerodynamic model for Type I and II, and linearized aerodynamic model for Type III. The drivetrain has been model either as a single-mass shaft model or as a double-mass shaft model. Most of the dynamic models of wind turbines consider the wind torque only as a function of the wind velocity, and they neglect the vibrations of the blades as an excitation torque. Therefore, a dynamic model that includes the aerodynamic power, the torque produced by the deflection of the blades, the vortex-induced vibrations of the blades and the torque caused by the eccentricity of the center of mass represents the excitation torque. The dynamic model of the wind turbine is a multibody dynamic model with six degrees of freedom. The blades are represented as a two lumped-masses, the torsional response of the main rotor is described as a single torsional mass, which is connected to the electric generator by a gearbox. The gearbox is represented as a double-shaft model, and the gear mesh is simulated with a nonlinear torsional stiffness. The generator is described as another torsional mass. The torque produced by the wind is calculated using QBlade for different pitch angles. The dynamic parameters of the blade were determined experimentally, and it was found that the blade has only two dominant vibration modes. For this reason, the blades were modeled as two lumped-masses. It was found that the vortex-induced vibrations modify the torsional vibrations of the generator and they are an extra source of perturbations for the electric generation, and they depend on the wind velocity and the pitch angle.