Active Gearing System for Wind Turbines

Abstract

The purpose of this research paper is to investigate the possibility of improving the efficiency of wind turbines by taking advantage of the wind speed variability. An active epicycloids gearbox system allowing a variable speed at the input shaft and delivering a constant speed at the output shaft is proposed herein. The gearing system consists of an assembly of spur and ring gears run and controlled by an electrical motor. The system acts as a continuously variable transmission (CVT) between the wind turbine hub and the electricity generator which requires an entry speed corresponding to an electrical grid frequency of 60 Hz. The active gearing system is designed using CAD software, and the gearing design theory is used to dimension the proposed epicycloids system. The kinematic gearing theory is used to establish the different gearing ratios of the system, and the kinematic velocity relationships between the gearing system stages. The forces and torques acting on the gearing system are computed using the equilibrium equations. Ideally, the electrical power consumed by the regulating motor system is minimal so that a maximum percentage of the generated electrical power is supplied to the electricity grid. The advantage of this gearbox configuration is that the power consumed by the regulating motor will be theoretically close to zero when the wind speed is about 10.5 mph, which is the average wind speed for many areas where wind turbines are installed. As the wind speed moves away from its mentioned average, the gearbox electrical controls activate a regulating motor to secure a constant speed at the generator input. Currently, a prototype of the proposed system is under tests and experimental data has already shown the constancy of the angular velocity at the generator input. The measurements of the mechanical power distribution between the different components of the system are still underway. A prony-break system is currently used for this purpose. It is expected that within a defined range of the hub angular velocities, the power absorbed by the regulating motor remains a small fraction of the power delivered by the electricity generator.