Active Conical and Planetary Gearing System for Wind Turbines

Abstract

The purpose of this research project is to explore the possibility of harvesting the energy of the wind by taking advantage of higher wind speeds. Two active gearbox systems allowing a variable speed at the input shaft and delivering a constant speed at the output shaft are currently being built and tested. The first system consists of an assembly of spur, planetary, and ring gears run and controlled by electrical motors. The second system consists of an assembly of a conical shaft, a wheel, and a set of centrifugal masses. The two gearing systems can act separately as a continuously variable transmission (CVT) between the wind turbine hub and the electricity generator which requires an entry speed corresponding to a frequency of 60 Hz. The two gearing systems are designed using the SolidWorks CAD software for modeling and simulation, and the gearing design theory is used to dimension the required spur, planetary and ring gears for the first proposed system. Betz’s law associated with appropriate and realistic wind turbine efficiency is used to estimate the wind power transferred to the turbine hub. The law is also used to determine the hub angular speed as a function of the wind speed. The kinematic gearing theory is used to establish the different gearing ratios of the planetary system, and the kinematic relationships between the system stages. The forces and torques acting on the first and the second systems are computed using the equilibrium equations. The speed ratios are calculated for the first and second system using the kinematic theory. Ideally, the electrical power consumed by the regulating motor for the first system is minimal so that a maximum percentage of the generated electrical power is supplied to the electricity grid. For the second system the totality of the harvested power is transmitted through the conical/wheel system. For the planetary system, when the wind speed deviates from a certain optimum value, the electrical controls activate a regulating motor to guarantee that the generator input speed remains constant. Currently, a prototype of a more robust planetary gearing system than a previously made one is under construction while a newly constructed conical system is under experimental testing. Running speeds, torques, power transfer and distribution for the two systems will be measured. The generated electrical power is measured using different load resistances and compared to the electrical power consumed by the regulating motor for the planetary system. The torques are measured using a prony brake system while the angular speeds are measured using tachometers. It is expected that the power consumed by the regulating motor for the gearing system will remain a small percentage of the power supplied to the grid for various hub input speeds.