Power controller design and damping improvement of torsional oscillations in the 710 kW DFIG based wind turbine installed at the Binalood site

The system under study in this paper is a real 710 kW DFIG based wind turbine installed in the binalood site. Based on the measurements and observations of the turbine, at high wind speeds, electromechanical oscillations with frequency of 2 Hz apear on the mechanical system leading to turbine vibration. Control of the wind turbine is carried out based on the power control through a predefined power-speed curve provided by the wind turbine manufacture. The purpose of this paper is to find out the nature and reason of the above mentioned electromechanical oscillations. Hence, the paper first deals with the power control design based on the corresponding power-speed curve. Then, mechanical modes of the system under different operating conditions and wind speeds are extracted. It is shown that at some operating points, low frequency oscillations with frequency of 2 Hz appear on the generator power, generator speed and shaft torsional torque. Next, for improving the damping of the torsional modes, an auxiliary stabilizer control, known as torsional oscillations stabilizer (TOS), is proposed. At the end, simulation results for the system under study are presented.