Modeling and control of variable-speed wind-turbine drive-system dynamics

When designing control for variable-speed wind turbines, one deals with highly resonant, nonlinear dynamic systems subject to random excitation, i.e., wind turbulence. This requires good knowledge of the dynamics to be controlled, particularly when combined with the increasingly common “soft” concept of lightweight, flexible constructional components; it creates cost advantages compared to more material-consuming rigid constructions, but also results in low frequency structural eigenfrequencies, some of which may appear in the bandwidth of closed-loop operation. For this article, system-identification experiments have been performed on an existing 400 kW, variable-speed, horizontal-axis wind turbine using various identification schemes. The identification results have then provided numerical values of the parameters in a physical model of the drive system. The acquired model has been used for design and evaluation of a number of linear and nonlinear control schemes for wind-turbine speed regulation