-Wind energy is a viable option to complement other types of pollution-free generation. In the early development of wind energy, the majority of wind turbines were operated at constant speed. Recently, the number of variable-speed wind turbines installed in wind farms has increased and more wind turbine manufacturers are making variable-speed wind turbines. This paper covers the operation of variablespeed wind turbines with pitch control. The system we considered is controlled to generate maximum energy while minimizing loads. The maximization of energy was only carried out on a static basis and only drive train loads were considered as a constraint. In medium wind speeds, the generator and power converter control the wind turbine to capture maximum energy from the wind. In the high wind speed region, the wind turbine is controlled to maintain the aerodynamic power produced by the wind turbine. Two methods to adjust the aerodynamic power were investigated: pitch control and generator load control, both of which are employed to control the operation of the wind turbine.Our analysis and simulation shows that the wind turbine can be operated at its optimum energy capture while minimizing the load on the wind turbine for a wide range of wind speeds. INDEX TERMSWind turbine generator, renewable energy, pitchcontrolled, variable speed.

No abstract

In this paper, we illustrate the effect of adding a hypothetical 100-MW doubly fed induction generator (DFIG) wind power plant to a weak transmission system. The effects of various wind plant load factors (100, 60 and 25% of nameplate rating) are investigated. System performance is compared to a 100-MW conventional synchronous generator interconnected at the same location. The conventional generator is installed some distance away. The simulations demonstrated that DFIG generators provide a good damping performance under these conditions. These results support the conclusion that modern wind power plants, equipped with power electronics and low-voltage ride-through capability, can be interconnected to weak power grids without reducing stability. To conduct the studies, we selected an area of the Western Electricity Coordinating Council power system that is electrically far from major generation centers and is weakly connected to the bulk transmission system. The area contains large motor loads. We observed the dynamic response of large motors in the vicinity, especially their ability to ride through fault events. The studies were conducted using positive sequence phasor time-domain analysis.Index Terms-Low voltage ride through, power system, renewable energy, stability, variable-speed generation, weak grid, wind energy, wind farm, wind power plant, wind turbine.

No abstract

These guidelines are intended to be a design aid for wind turbine designers. The complete list of guidelines is provided below. • DG01 Loads Analysis • DG02 Strength Analysis • DG03 Yaw and Pitch Rolling Bearing Life Design Guideline • DG04 Gearbox Specification • DG05 Control and Protection System Specification and Design All of these documents-with the exception of the present document (DG03)-are in draft form and are available only by request sent to NREL, Sandy.Butterfield@NREL.Gov. Modern wind turbines use large turntable bearings at the root of each blade to enable pitch angle changes and thus aerodynamic performance and load control. Yaw bearings are used for angular realignment of the nacelle into the predominant wind direction. These applications require long periods in nearly stationary positions with large stochastic loads. Due to this demanding load environment and the fact that bearings exist in the critical load path, their design becomes critical to the safety and reliability of most turbine designs. This document attempts to introduce modern bearing-design practice and its relation to the unique requirements of wind turbine applications. The fundamental theory presented here is available in other textbooks referenced in this document, and included in the References section found at the end of this report.