Damping tie-line power oscillations by modulation feedback of wind generators

This paper uses the power modulation capability of wind generators for damping tie-line power oscillations. The type of wind generator investigated is the permanent magnet synchronous generator (PMSG) connected to the power grid through a dc link. First, the paper develops a small-signal aggregate model for the wind generator. Subsequently, three modulation signals are investigated in order to provide effective power modulation: the PMSG speed reference, the rotor blade pitch angle and the dc link voltage. The latter is a novel approach that utilizes the energy stored in the dc link capacitors in order to modulate the power injected into the grid. The paper investigates the relation between the wind turbine and PMSG dynamics and the ability of each modulation loop to provide effective damping. A design method of the feedback loops based on the damping torque concept is demonstrated in the paper. Analytical results on a two-area power system show that wind generation can enhance the system dynamic stability by damping tie-line power oscillations. The analytical results are verified through time-domain simulations of a detailed 3-phase model of the system. The proposed dc link voltage modulation is shown to be a very effective means to provide power modulation in dynamic conditions.