Control of a variable ratio gearbox and mechanical brake to maximize wind energy production

The purpose of the authors' research is to develop a variable ratio gearbox (VRG) that enables discrete variable speed operation for fixed-speed wind turbines in the production range of 50 to 500 kW. Previous work suggests that this device can increase power production by 7% over the original configuration. The current study further increases the wind capture by applying control to the VRG and mechanical brake. In this technique the selected gear ratio produces torque slightly above the level that is required, by the generator, for full power. This excess torque is removed through the mechanical brake, and full load production is realized simultaneously. This paper discusses the framework and decision-making protocol used to control these two subsystems. The control design process uses dynamic programming to insure maximum energy production while conserving brake liner. System performance is simulated for twenty sets of wind data that cover a wide range of wind conditions. The results demonstrate that full production can be achieved across greater ranges of wind speed, and can increase electrical production by an average of 10% for the sites considered.