Stability analysis of an adaptive torque controller for variable speed wind turbines

Variable speed wind turbines are designed to follow wind speed variations in low winds in order to maximize aerodynamic efficiency. Unfortunately, uncertainty in the aerodynamic parameters may lead to sub-optimal power capture in variable speed turbines. Adaptive generator torque control is one method of eliminating this sub-optimality; however, before adaptive control can become widely used in the wind industry, it must be proven to be safe. This paper analyzes the stability of an adaptive torque control law and the gain adaptation law in use on the Controls Advanced Research Turbine (CART) at the National Renewable Energy Laboratory's National Wind Technology Center.