Inertial response from wind turbines: the impact on structural loads

This works evaluates the impact on structural loads of DFIG wind turbines providing inertial response while operating at rated power. The approach is to use an integrated simulation environment to model the most important electrical, structural, and control dynamics. Estimation of the impact is done in terms of 1-Hz equivalent loads, and maximum-minimum loads. It is observed that some structural loads are significantly affected. Therefore the trade off between the amount of inertial response and the cost of loads imposed should be assess from an statistical perspective. Introduction Inertial response from wind turbines can contribute to maintain short-term stability of the power system. In power systems with large amount of power produce by wind power plants, such feature will be relevant. Since the work in [1] there are a number of proposed control strategies in the literature. Nowadays many manufacturers already offer wind turbines with the capability of providing inertial response [2,3]. However, grid codes to rule this requirement are not yet in place. Furthermore, practical implementation of inertial response in variable speed wind turbines may be impose considerable loading on wind turbine components. This works evaluates the impact on structural loads of DFIG wind turbines providing inertial response. The approach is to use an integrated simulation environment. Namely, the objectives of this work are • to estimate the impact on wind turbine structural loads providing inertial response, • to compare the response of the power system with, and without inertial response from wind turbines and • to demonstrate the capabilities of an integrated simulation approach. The most important dynamics of power system, electrical machine, control, structure, and aerodynamics are modeled in an integrated simulation environment. The software tools integrated in this environment are (1) aeroelastic software (HAWC2) and (2) Matlab/Simulink. Technical details of the interfacing of these software can be found in other publications of the authors. The following section, describes the integrated analysis model that consists of a power system model for frequency control and a wind power plant model as indicated in Figure 1. The wind power plant is modeled by the aggregated response of a wind turbine model. The power system, wind turbine controls, wind turbine generator and wind turbine aggregation are modeled in Matlab/Simulink while the wind turbine structure and aerodynamics are modeled in HAWC2. The Results section describes the numerical simulation results, such as the response of the power system frequency, blade angle and generator torque, as well as some of the structural loads that are significantly affected. A table of normalized equivalent and maximum-minimum loads gives a picture of the impact on all structural loads that are are normally used for design verification (blade root, low-speed shaft, tower top and tower bottom moments). Finally the conclusions of this work are gathered in the Conclusions section.