Application And Mechanism Research On Smart Load Control System Of A Large-Scale Wind Turbine Blade

Since offshore wind power has the advantages of high wind speed, less dust, stable and suitable for large-scale development and so on, the global wind farm construction has gradually spread from the land to the sea. In order to reduce the unit cost of electricity gradually, the size of the offshore wind turbine blades has became more and more larger. Recently the VI64-8.0 MW wind turbine impeller, the diameter of which has reached about 160 m, has successfully generated power. With the size of the wind turbine blades growing, its flexibility has been enhanced and the wind speed difference along the impeller plane becomes larger, which will weaken the aeroelastic stability, increase the loads, and consequently tends to blade damage. Especially for offshore wind turbines, the construction and maintanence costs of which are very high, therefore making reliability requirements higher, and the key of improving reliabity is to reduce the fatigue loads and extreme loads. However, nowadays the wind turbines depend on the collective pitch technology to reduce these loads. But this technology has been unable to cope with the local random fluctuations of the load on the blade because of its slow movement, huge energy consumption and other shortcomings.In order to develop more effective load suppressing methods, recently the "smart rotor" concept borned in the helicopter has been successfully introduced to the field of wind turbines by some researchers. It is an active type of flow control technolog, which can change the local aerodynamic surface deformation through a combination of sensors, controllers and actuators. Its principle is to adjust the local airfoil lift by changing the surface deformation and further to reduce the loads on the blades. Among many "smart rotor" actuators, the deformable trailing edge flap (DTEF) has been recognized as the most promising device because of its fast response, wide adjustment range, small flow disturbances etc. For this area, our group has successfully made the wind turbine simulation platform based on DTEF, and also discussed its control effect under normal turbulent or extreme wind shear wind conditions.Based on our previous works, for the purpose of industrial application, this paper further carries out the followings:Firstly, this paper analyses the impact of the four main DTEF parameters, i.e center position Rf/R, spanwise length ratio Lf/L, chordwise length ratio Cf/C and maximum defection angle |φf,max| on the effectiveness of DTEF control system. The results show that:in general, with the increase of these parameters, the DTEF control effect increases substantially. But the exception is that the control effect of the DTEF on the blade tip is very different from before and after the rated wind speed.Secondly, this paper chooses a typical set of DTEF parameters, and analyzes the role of DTEF control system uder the ECD wind model, which represents a extreme coherent gust with direction change and specified in IEC standard for checking the load status of the wind turbine on the power production condition. The results show that:the DTEF control system can effectively reduce the load fluctuations due to the extreme changes of wind speed and wind direction. In particular, the fluctuations of the root flapwise moment and the blade tip deflection can be reduced by 30%.At last, this paper discusses the effects of three practical senors on the DTEF control system, i.e acceleration, root flapwise moment and tip deflection. The results show that:the root flapwise moment signal is better than accelerometer, which is better than blade tip deflction signal considering the DTEF control effect.In addition, this paper discusses the flow control mechanism due to DTEF control through detecting the changes of the blade flow-structure coupling characteristics. The results show that: the perturbed DTEF activation the nearby aerodynamic normal force on the blade are in anti-phase or opposite movement, thereby disrupting the good synchronization between the normal force and the local acceleration, increasing the damping ratio of the blade flow-structure system, therefore this DTEF control system can effectively suppress the fluctuation of the impeller and other parts of the drive train loads.