On the Severity of Wind Turbine Generator Speed Peaks in Response to Particular Gusts

Abstract

An objective of a wind turbine control system is to avoid generator over-speeds that can trigger  turbine shutdown. This work aims to study the wind and the control actuator signals for a two-bladed downwind turbine to assess generator speed peaking behavior. Peaks in generator speed are often observed when there is a lull in wind speed followed by a rising gust. A ‘gust measure’ is used to quantify the severity of such peaks. Field data from the Segmented Ultralight Morphing Rotor demonstrator turbine tested at the US National Renewable Energy Laboratory is used for this assessment. Nacelle wind speed is analyzed for simulation and field cases to determine a gust measure for particular sequences of wind inputs preceding peaks in generator speed. The gust measure tested under varied wind conditions to estimate peaks in generator speed shows a good correlation between high values of the gust measure and peak occurrences in generator speed. A novel modified gust measure that accounts for the proximity to a control transition from region 2 torque control to region 3 blade pitch control is developed to further improve the correlation. We conclude that gust measures of the forms described here can be used online with advanced control strategies to predict and mitigate generator speed peaks.