An extended inertia and eigenfrequency emulation for full-scale wind turbine nacelle test benches

The main causes of wind turbines failures are mechanical and electrical drive train components [1]. Since isolated simulation studies seem not to sufficiently reproduce load situations in the fully assembled and operated system, wind industry pays more and more attention to wind turbine System Test Benches. They allow for detailed load analysis within the complete drive train system and also for controller tests. For both investigations drive train dynamics of the wind turbine generator (WTG) are of high relevance. This dynamic behavior is mainly determined by the rotor´s inertia which, due to its size, has to be dismounted for System Test Bench tests. By that, the dynamics of the remaining drive train change significantly. In order to still operate the WTG controller without modifying it and to allow for representative load analysis a Hardware-in-the-Loop (HiL) Controller needs to reproduce the realistic drive train behavior at the System Test Bench. This paper proposes a control concept which emulates the missing rotor related inertia as well as the drive train and the coupled rotor-drive train related eigenfrequencies which are both crucial for load analysis as well as controller tests. The proposed concept consists of a virtual spring-damper-system combined with a subsidiary state feedback controller. The controller synthesis is conducted using a quadratic norm. The simulation results show that the eigenfrequencies can be reproduced with less than 2% error. When time-discrete operation is considered, the results are slightly downgraded, so that alternative synthesis procedures need to be investigated in the future. The method proposed in this paper is based upon an experimentally verified inertia emulation method [2]. Furthermore the simulation models used throughout this simulation study are experimentally validated models of a 1MW System Test Bench [3] at the Center for Wind Power Drives of RWTH Aachen University.