IMPLEMENTATION OF A TWO-AXIS SERVO-HYDRAULIC SYSTEM FORFULL-SCALE FATIGUE TESTING OF WIND TURBINE BLADES

摘要

Recently, the blade fatigue testing capabilities at NREL were upgraded from single-axis to twoaxisloading. To implement this, several practical challenges were addressed, as hardwarecomplexity increased dramatically with two actuators applying the loads at right angles to eachother. A custom bellcrank was designed and implemented to minimize the load angle errorsand to prevent actuator side loading. The control system was upgraded to accept load anddisplacement feedback from two actuators. The inherent long strokes uniquely associated withwind turbine blade-tests required substantial real-time corrections for both the control and datasystems. A custom data acquisition and control system was developed using a NationalInstruments LabVIEW platform that interfaces with proprietary servo-hydraulic softwaredeveloped by MTS Corporation. Before testing, the program is run under quasi-static (slowspeed) conditions and iterates to determine the correct operational control parameters for thecontroller, taking into consideration geometry, test speed, and phase angle errors between thetwo actuators. Comparisons are made between single-axis and two-axis test loads using actualtest load data and load uncertainties are qualitatively described. To date, two fatigue tests havebeen completed and another is currently ongoing using NREL’s two-axis capability.