Large wind turbines typically have variable rotor speed capability that increases power production. However, the cost of this technology is more significant for small turbines, which have the highest cost-per-watt of energy produced. This work presents a low-cost system for applications where cost and reliability are of concern. The configuration utilizes the fixed-speed squirrel cage induction generator. It is combined with a variable ratio gearbox (VRG) that is based on the automated-manual automotive transmission. The design is simple, low cost, and implements reliable components. The VRG increases efficiency in lower wind speeds through three discrete rotor speeds. In this study it is implemented with active blades. The contribution of this work is a methodology that synthesizes the selection of the gearbox ratios with the control design. The design objectives increase the power production while mitigating the blade stress. Top-down dynamic programming reduces the computational expense of evaluating the performance of multiple gearbox combinations. The procedure is customizable to the wind conditions at an installation site. A case study is presented to demonstrate the ability of the strategy. It employs a 300 kW wind turbine drivetrain model and uses wind data as an input. The results suggest a VRG can improve energy production in Region 2 by roughly 10% in low and high wind speed regions. The stress also increases in Region 2 as the power increases. However, the stress in a range of Region 3 decreases through the optimal selection of gear combinations.
