Robust Linear Parameter-Varying Control for Multi-Megawatt Wind Turbine Testing

Wind turbine testing is of great relevance for the wind industry to reduce the levelized cost of energy. For this purpose, hardware-in-the-loop simulators have been developed within the last years and the concept has been validated using multi-megawatt state-of-the-art nacelles. From the experimental experience of several years, different physical phenomena have been identified, which are insufficiently and unsystematically handled by state-of-the-art control algorithms. These effects include multi-physical couplings, nonlinear friction, and periodic disturbances due to unbalanced masses. We analyze the test bench control problem by means of linear parameter-varying (LPV) control theory and arrive at a formulation with the scheduling parameters rotation speed and torque. Based on experimental data, we derive a quasi-LPV plant model for which controller synthesis is conducted. In particular, the superior performance of different self-scheduled dynamic output feedback LPV controllers compared to a standard robust controller is shown. By using parameter-dependent Lyapunov functions, we guarantee both stability and performance with respect to scheduling parameters with a bounded rate of variation. Furthermore, we propose an approach for systematically handling highly dynamic fault cases on a test bench by reconfiguring controller properties through the introduction of fault specific dynamic weighting functions. A converter failure test case is analyzed in simulation to show the benefits of the here proposed controller design.