Wind turbine control using a gearless epicyclic transmission

A recurrent problem in energy production by means of wind turbines is how to keep a constant angular velocity at the shaft driving the alternator in the presence of a randomly varying turbine angular velocity. The latter is caused by the random nature of the wind velocity. Proposed in this paper is an innovative two-degree-of-freedom mechanism, with the morphology of a differential gear train, but without gears. The latter are replaced by cam-roller pairs, which offer many advantages over gears: low friction, low backlash and much higher stiffness. The mechanism, dubbed pitch-roll wrist, was originally developed as a robotic wrist for pitch-roll generation. It is shown in the paper that the mechanism can effectively control its pitch velocity in the presence of a randomly varying angular velocity, which emulates that produced by wind on the shaft of a wind turbine. The pitch velocity, in turn, emulates that of the shaft driving the alternator. The control algorithm, based on a PID controller, was tested on an experimental testbed. Results show an effective angular velocity control.