Effect of Sag Voltages From Wind Turbines on DC Link Capacitors of Adjustable Speed Drives

Abstract

The dependence of the instantaneous generation output of wind turbines on wind speed and wind unevenness as a geographical phenomenon have made wind generators unpredictable power plants. Fluctuations in wind speed can lead to fluctuations in the power fed into the grid by the wind farm. As a result of these fluctuations, transient over voltages occur in the grid and especially in loads near the Point of Common Coupling (PCC). In this paper, the causes of over voltages in wind turbines were studied and simulated in Simulink MATLAB. Their negative effects on reducing the lifetime of electrolytic capacitors used in Adjustable Speed Drivers (ASD) induction motors were studied. As a result of the thermal stresses caused by these over voltages, the predicted lifetime of one type of electrolytic capacitor examined is reduced by 50% from about 18,000 hours to about 9,000 hours.