Control design for mechanical hardware-in-the-loop operation of dynamometers for testing full-scale drive trains

Advanced testing methods are becoming more and more prevalent to increase the reliability of wind turbines. In this field, dynamometers that allow for system level tests of full-scale nacelles will play an important role. Operating these test benches in a hardware-in-the-loop (HiL) set-up that emulates realistic drive train modes is challenging because of the relatively low stiffness of the load machines' drive trains. This paper proposes a control method for enabling the said operation mode. It is based on the idea that the HiL-controller overrides the present unrealistic dynamics and directly imposes desired realistic dynamics on the test bench. A solution for the control problem is given and applied in a design study with a generic wind turbine and a test bench model obtained from construction data of a real test bench. In the design study, the HiL-controller robustly imposes desired drive train dynamics on the test bench model. Despite measurement noise, unmodelled parametric uncertainty, and unmodelled delays, the first drive train mode is correctly reproduced. This is confirmed by a comparison with simulation results from a full servo-aero-elastic code. Furthermore, an implementation of the test bench model on a programmable logic controller showed the real-time feasibility of the proposed method.