Reproduction of five degree-of-freedom loads for wind turbine using equispaced electro-hydraulic actuators

Several improvements are proposed to enhance the capability of conventional wind turbine simulators since such simulators can only simulate the turbine shaft torque, or can partially generate the other five degree-of-freedom turbine loads in addition to the turbine shaft torque. In the improved wind turbine simulator, the real wind rotor and blades are represented by an equivalent rotating disc to replicate the turbine inertia effects. Twenty-four electro-hydraulic loading actuators are symmetrically distributed around this rotating disc and are controlled independently to reproduce the additional five degree-of-freedom turbine loads that can be described in the blade and hub coordinate systems. A loading decomposition strategy is also proposed to decompose such five-degree-of-freedom turbine loads into reference loading forces for each loading actuator by incorporating additional seven-degree-of-freedom dummy loads. A typical axial loading actuator is taken as an example for in-depth dynamic modeling and analysis. Two intrinsic pressure-sensed closed control loops and different pressure modes of this actuator are presented and analyzed in detail. The dynamic model of this typical loading actuator has been thoroughly validated by using experimental measurements. Simulation results have also demonstrated that the five degree-of-freedom turbine loads can be accurately reproduced by using such electro-hydraulic loading actuators. Therefore, the improved wind turbine simulator can fully simulate steady-state and dynamic turbine loads with good accuracy and can expedite the system-level loading tests that are critical in increasing turbine reliability and offering high confidence system design.