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

Abstract

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 Hardwarein-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-dampersystem 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 1 MW System Test Bench [3] at the Center for Wind Power Drives of RWTH Aachen University.

Impact of Multi-Physics HiL Test Benches on Wind Turbine Certification

“…A similar approach for MHiL is introduced in [10], but restricted to simulation results for validation. An emulation of rotor inertia and related eigenfrequencies was first introduced in [11], where a state feedback controller shifts the eigenfrequencies of the test bench to the desired locations in the complex eigenvalue plane. The authors of [12] use model-based control, namely an internal model control, and suggest a two-step procedure to design the HiL control algorithm, which also allows eigenfrequency emulation.…”

Considerations for testing full-scale wind turbine nacelles with hardware-in-the-loop

“…However, when mounted on a test bench, the test article is missing the rotor (hub and blades) and the tower which significantly alters its boundary conditions thereby changing the dynamic characteristics of the drivetrain leading to responses that are different from field testing. Several efforts have been made to address these differences and develop control techniques to emulate the missing inertia and replicate eigenfrequencies such that field testing can be better reproduced on a test bench [3][4][5][6][7].…”

Comparison of HiL Control Methods for Wind Turbine System Test Benches

“…In the field, the drive train of a WT oscillates in its eigenfrequencies due to the flexible rotor and turbulent inflow. A 3-mass oscillator was shown to sufficiently model the first two rotational eigenfrequencies and thus the drive train of a WT (Jassmann et al (2015)). Similarly, modeling the drive train of the DUT on a STB is enabled by a 3-mass oscillator.…”

“…ing. Extensions to the IE method allow eigenfrequency emulation and are based on pole placement for state feedback control (Jassmann et al (2015)) or a WT reference model (Neshati et al (2016b), Jassmann 2018 Throughout the comparison of different HiL control approaches, the same HiL system architecture shown in Fig. 1 is used.…”