Characterizing wind turbine drivetrain nonlinearities for hybrid nacelle tests

The increasing size of modern wind turbines presents significant challenges to existing nacelle testing infrastructures that are unable to reproduce the required extreme loads, achieve the necessary dynamic load bandwidth and provide increased power capacity while maintaining escalating costs of testing. The novel hybrid nacelle testing approach developed at Fraunhofer IWES aims to resolve some of these challenges. It combines high-fidelity virtual models with partial load physical testing to predict full load responses on a nacelle test bench. One of the primary challenges related to this new testing approach is ensuring that the underlying models accurately capture the complex nonlinear interactions and behaviors that can occur under full load conditions. This paper investigates the sources of nonlinearities in the response of the drivetrain during steady-state parasitic load tests on a nacelle test bench. Multiple system responses are investigated, and the corresponding type of nonlinearity is classified. A full understanding of these critical nonlinearities in the system will enable the development of a suitable modeling approach and partial test criteria required to perform hybrid nacelle testing.