Optimized Feedback Control

Optimized Feedback Control (OFC) is one of the four major control components of the integrated wind turbine control concept SucCon, which is being developed in the SenterNovem research project number EOS LT02013 “Sustainable Control: A new approach to operate wind turbines”. The aim of the OFC task is to minimize the loads on important wind turbine components (drive-train, blades, tower, and nacelle) in order to reduce the cost of energy. Lower loads make the use of lighter components possible and allow achieving further upscaling of offshore wind turbines. Since tower and drive-train damping control loops already pertain to state-of-the-art technology, the focus within OFC is put on the development and implementation of blade load reduction algorithms using individual pitch control (IPC). 

Although IPC control has also already received some attention by the scientific community, its practical application remains restricted due to the necessity to comply with the actuator limitations, expressed as position, velocity and acceleration constraints on the blade pitch signals. For that reason, within the OFC task special attention has been paid to the development of an effective approach to incorporate these actuator constraints into the IPC algorithm while at the same time retaining guaranteed stability. In implementing the constraints into the IPC algorithm, priority is given to the baseline rotor speed controller so that only the actuation freedom that is not being used up by the baseline controller can be consumed by the IPC for reducing blade loads.

Furthermore, investigation of the effects of rotor imbalance (resulting from imperfections in the blade profiles, blade mass and pitch setting caused during manufacturing, assemblage or due to icing) on the performance of the IPC algorithm has shown that unbalance can significantly deteriorate the performance of the IPC loop. A novel IPC algorithm has been developed that compensates for the rotor unbalance by pitching the blades to some quasi-static pitch angles (different for each blade) in such a way.

Publications

Control design based on aero-hydro-servo-elastic linear models from TURBU (ECN)
Engelen, T.G. van
ECN-M--07-054; Proceedings of the European Wind Energy Conference (EWEC 2007), Milan, Italy, 7-10 May, 2007.

Design model and load reduction assessment for multi-rotational mode individual pitch control (higher harmonics control)
Engelen, T.G. van
ECN-RX--06-068;  Proceedings of the European Wind Energy Conference (EWEC 2006), Athens, Greece, 27 February, 2006.

Exploring the limits in individual pitch control
Kanev, S.K.; Engelen, T.G. van
ECN-M--09-053; Proceedings of the European Wind Energy Conference (EWEC 2009), Marseille, France, 16-19 March, 2009.

Feedback-feedforward individual pitch control for wind turbine load reduction
Kausihan Selvam, Stoyan Kanev, Jan-Willem van Wingerden, Tim van Engelen, and Michel Verhaegen,
ECN-W--09-029; International Journal of Robust and Nonlinear Control, 19(1), pp. 72-91, 2008.