Wind turbine envelope protection control over the full wind speed range

Ensuring safe operation at all times and in all conditions is one of the primary goals of wind turbine control systems. This paper presents a novel approach for wind turbine control based on the concept of envelope riding. The proposed approach utilizes on-line numerical optimization to predict at each time instant the extremal wind speed that would lead the machine to encounter the envelope of its safe operating range. Based on this extremal condition, control inputs are computed that maintain the response within the safe region at all times, at the most riding its boundary but without ever leaving it. The method is capable of keeping the machine within its safe envelope within the entire range of operating wind speeds, including both rated and cut-out conditions. The new method is verified with the help of numerical simulations conducted with a high-fidelity aeroservoelastic environment. Comparisons are made with standard control algorithms for the prevention of excessive loading, including peak-shaving and soft cut-out schemes. Results illustrate the ability of the proposed approach in reducing loads and improving power output.