Abstract
This paper presents a fixed-switching frequency of direct reactive power control, called modulated hysteresis-direct reactive power control (MH-DRPC), for a variable speed wind turbine-based doubly fed induction generator (DFIG). Combination of two techniques, i.e. reactive power control-based fuzzy logic control and modulated hysteresis (MH) direct torque control, is the principle of the proposed strategy. The main advantage of this methodology is that the switching frequency of the converter switches is constant, where the major drawback of the classical DRPC is eliminated (the variable switching frequency). This new methodology aims to achieve sinusoidal forms of generated AC current with a constant frequency, ensure minimal current total harmonic distortion (THD), and minimum output voltage ripple irrespective of the wind speed fluctuations. This research work is aimed primarily at analyzing the performances of the new MH-DRPC, taking into account certain constraints that reflect the true working of wind turbine generators, such as the random wind speed behavior and variable reactive power demand. This allows analyzing all operation modes of DFIG, with an emphasis on synchronous and over-speed modes. A comparison with a classical DRPC is made to underline the effectiveness of the suggested approach. The MPPT algorithm and the pitch angle control are invested to optimize the captured wind power. Simulations of the proposed method are made under Matlab/Simulink. The simulation results revealed significant improvements over the classical DRPC in the following characteristics: a significant reduction in current THD supplying the AC grid (98.29%) and a good dynamic response with a significant reduction of ripples of electromagnetic torque (66.67%), rotor flux (42.67%), generated current frequency (96.70%), local reactive power compensation (50.23%), and generated active power (26.34%). In addition, the suggested MH-DRPC technique is extremely robust to machine parametric changes and random variations in references command.