Modelling and Analysis of DFIG Wind Turbine Harmonics Generated in Grids

In this paper an analytic technique for modelling harmonics is proposed for a DFIG wind turbine connected to the grid. An algorithm based on Hilbert transform for the analysis of harmonics in power systems is developed. The simulation results prove the effectiveness of the Hilbert Transform (HT) for power harmonic analysis in DFIG wind turbine connected to a grid. Index terms - Harmonic Analysis, Hilbert transform, power factor I. INTRODUCTION Wind energy is becoming a promising source of renewable energy. Technology has made it possible to implement variable speed wind turbines that are more efficient than fixed speed wind turbines. To utilize wind power generation efficiently one of the most reliable system is grid connected doubly fed induction generator. The DFIG brings the advantage of utilizing the turns ratio of the machine, so the converter does not need to be rated for the machine's full rated power. The rotor side converter (RSC) usually provides active and reactive power control of the machine while the grid-side converter (GSC) keeps the voltage of the DC-link constant. A typical configuration is shown in Figure 1. In this structure the wind turbine transformer is delta star- wired with ungrounded star point. Such a transformer blocks zero sequence currents. (1) DFIG controller design considerations have generally concentrated on providing an adjustable operating speed to maximize turbine power output, maintaining the required generator terminal voltage or power factor, and controlling the generator torque to match that of the wind turbine.