Investigation On Smart Load Control For A Large-scale Wind Turbines Using Deformable Trailing Edge Flap

As we know, with the fast development of wind energy, especially the rising of offshore wind energy, it’s a trend for the size of wind turbine to grow up. Wind turbines at rated power of8-10MW with a diameter up to160m are developing around the world, and it’s even said20MW turbines with a diameter of240m are feasible. On one hand, the larger a wind turbine is, the more flexible blades will be, which will result in more complicated loads on wind turbine; on the other hand, the larger diameter of wind turbine, the more variable wind across the rotor disk will be, it will bring substantial fluctuating loads across the rotor disk, which cannot be addressed solely by pitching the whole blade at a time. However, in order to reduce the cost of energy, especially for offshore wind energy, the turbines should have higher capacity to bear both fatigue and extreme loads, should have longer life with less maintenances. Therefore, it’s essential to develop an innovative technology, which will reduce load on large-scale wind turbine effectively, which can result in a significant reduction in cost energy by enhancing system relaibility, reducing cost of maintenance and extending the life of turbines.To this end, the concept of "smart rotor control" emerges. It drives local aerodynamic surfaces through a combination of sensors, actuators and controllers, and thus provides a higher load control capacity. Among various active or passive aerodynamic devices, the deformable trailing edge flap is treated as one of the most efficient candidates, characterized by its positive performance, fast response, small size and low flow disturbance etc., so this paper mainly focus on the design and investigation of smart load control system for large-scale wind turbine by using deformable trailing edge flap.Based on the series open source code, FAST, Aerodyn etc., combined with Matlab/Simulink, this paper primarily developed a new aero-servo-elastic platform for implementing smart load control system. Smart load control was applied to an Upwind/NREL5MW reference wind turbine to reduce fatigue and extreme load, under various turbulent and extreme operating wind conditions in accordance with the IEC, and the effects on other crucial properties, such as generator power, pitch system and tower load, were investigated. At last, the assumption of quasi-steady aerodynamics of airfoil with deformable trailing edge flap was evaluated, and the aero-elastic physics of smart load control were discussed by analyzing interaction of incoming wind, blade and trailing edge flap. In order to discover the better performance of the smart load control system, the effect of different configurations of deformable trailing edge flap were investigated, such as locations of flap on the blade, spanwise length of trailing edge flap, chordwise lengths of flap, the maximum range of deformable angles of flap. At the chosen typical configuration of flaps, the energy needed to activate the flaps is roughly estimated.It shows that the designed load control system in this paper not only reduced fatigue and extreme load on blades under turbulent and extreme wind cases successfully, but also alleviated loading on other components, such as tower, shaft and yaw bearing, at the same time, it results in less wear in pitch system and obtained steadier output. Investigation on flow-blade-DTEF interaction found that smart control effectively turns the strong synchronized interaction into a much weaker one, implying an enhanced dissipation of flow and blade vibration energies and their diminished correlation, which explained the remarkable load reduction at the dominant1P mode and subsequent those on drive-chain components. On the criteria of better capacity to reduce load, a typical configuration of deformable trailing edge flap was chosen, which is at70%of the blade from root, with spanwise length of20%blade length, with chordwise lengths of10%flap length, with a maximum range of deformable angle of±10°, in order to provide reference for practical use of smart load control with deformable trailing edge flap in the near future.