Variable speed wind turbine

Abstract: Due to its many advantages such as the improved power quality, high energy efficiency and controllability, etc. the variable speed wind turbine using a doubly fed induction generator (DFIG) is becoming a popular concept and thus the modeling of the DFIG based wind turbine becomes an interesting research topic. Fundamental frequency models have been presented but these models are often complex with significant numerical overhead as the power converter block consisting of power control, rotor side and grid side converter control and DC link are often simulated in detail. This paper develops a simple DFIG wind turbine model in which the power converter is simulated as a controlled voltage source, regulating the rotor current to meet the command of real and reactive power production. This model has the form of traditional generator model and hence is easy to integrate into the power system simulation tool such as PSS/E. As an example, the interaction between the Arklow Bank Wind Farm and the Irish National Grid was simulated using the proposed model. The model performance and accuracy was also compared with the detailed model developed by DIgSILENT. Considering the simplification adopted for the model development, the limitation and applicability of the model were also discussed in this paper.

Abstract: This paper introduces a method to improve the primary frequency contribution of grid connected variable speed wind turbine generators (WTGs). Using their energy reserve margins, deloaded WTGs are controlled to provide relief to the grid during depressed frequency conditions. The frequency support from individual WTGs is regulated based on the available reserve, which depends on the prevailing wind velocities. By continuously adjusting the droop of the WTG in response to wind velocities, its primary frequency response is significantly improved in terms of reduced stresses on WTGs during low wind speeds. The impact of variable droop operation on two aspects of WTG operation is investigated-primary frequency contribution and smoothening power fluctuations caused due to changes in wind speed. Also highlighted is the usefulness of this control when adopted by wind farms.

Abstract: This article considers an adaptive control scheme previously developed for region 2 control of a variable speed wind turbine. In this paper, the question of theoretical stability of the torque controller is addressed, showing that the rotor speed is asymptotically stable under the torque control law in the constant wind speed input case and L/sub 2/ stable with respect to time-varying wind input. Further, a method is derived for selecting /spl gamma//sub /spl Delta/M/ in the gain adaptation law to guarantee convergence of the adaptive gain M to its optimal value M*.

Abstract: This paper quantifies the capability of providing a short-term excess active power support of a commercial multi-megawatt variable speed wind turbine (VSWT) and generalizes the findings by considering different wind turbine (WT) physical parameters in a wider range from the example case. The paper also identifies some possible applications of it, in particular, in a hydro dominated system. To be able to quantify the system characteristic, a delay model of the studied hydro system is developed. Due to the fact that the initial power surge of a hydro turbine is opposite to that desired, the short-term extra active power support from a wind farm (WF) could be beneficial for a hydro dominated system in arresting the initial frequency fall, which corresponds to an improvement in the system temporary minimum frequency (TMF). The improvements in the TMF are calculated by using both the developed delay model and a detailed model, and the results show good agreement. It is shown that the WT under consideration can provide a 0.1 pu extra active power support for 10 s quite easily which is twice the Hydro-Quebec requirement.