Fluctuating characteristic and power smoothing strategies of WECS

Abstract

The electric power output of the wind energy conversion system (WECS) fluctuates owing to the inherent feature of the wind speed, which do harm not only to the power grid it connected into, but also to the lifetime of power converters. The electric power fluctuation characteristic of WECS is analysed in frequency domain under overall wind speed to facilitate the planning of distribution grids and to reveal the key factors influencing power fluctuation under different operation modes. The analysis results are well-validated by detailed simulations. On the basis of power fluctuation characteristic analysis, the power-smoothing schemes are carried out in different operation modes. In variable-speed mode, an enhanced optimal torque control is proposed for power smoothing. In constant-speed mode, the control bandwidth of speed loop or the slope of look-up table is decreased to smooth the electric power, and a feed-forward pitch control is proposed to prevent the wind turbine from exceeding safe speed. In constant-power mode, the suggested power-smoothing scheme is worked out. The analysis results and the proposed control schemes are verified by refined co-simulation platform based on GH bladed and real-time digital simulator.