Hardware-in-the-loop drive train control for realistic emulation of rotor torque in a full-scale wind turbine nacelle test rig

This paper presents a concept for hardware-in-the-loop (HiL) drive train control of a 10 MW full-scale ground test facility for wind energy converters(WEC). This is to enable realistic emulation of the missing rotor torque, in order to provide a realistic test environment under load conditions comparable to those in the field. The HiL framework consists of a dynamic rotor model coupled with the test rig drive train in a suitable structure. The goal is to apply a realistic torque on the main shaft of a device under test being comparable to that of an ideal WEC model. Therefore, accurate reproduction of the torque with respect to its dynamic and steady-state properties is required. Consequently, active vibration damping of the drive train is necessary due to the discrete mass structure of th e drive train and finite elasticity of the intermediate couplings, and also enough degrees of freedom is required to influence frequency response of the closed-loop system in and around the torsional modes. Hence, the drive train has been modelled and an estimation-based torque control strategy has been proposed taking into account torsional behaviour of the drive train and the virtual rotor. In the proposed state-space control structure, a linear-quadratic-gaussian regulator and a constrained model predictive controller (MPC) explicitly considering the actuator's physical limitation have been implemented, while the unmeasured state-variables are to provided by a time-varying Kalman filter. For an evaluation of the proposed approach, simulation results are provided and compared. Additional ly, interaction of the coupled dynamic subsystems is analysed and illustrative conclusions are made. Overall, the proposed HiL framework leads to an accurate rotor inertia emulation and enables reproduction of the virtual rotor's torsional mode.