Improving power quality by fed dfig converter with various switching techniques

In this paper, an integrated system of wind farm based on doubly fed induction generators (DFIGs) is modeled and simulated in Matlab/Simulink environment. To connect the wind farm based on DFIGs to the electrical grid, the grid code requirements should be achieved and as a result of the use of back-to-back converter interfacing the rotor winding with the grid causes harmonic distortion for voltage and current of this generator. Therefore, the waveforms of voltage and current of DFIG wind farm are investigated and improved from view point of power quality at all wind speeds using two different topologies of back-to-back converter connecting the rotor with the grid, namely two-level and three-level neutral point clamped (NPC), and also using several types of switching techniques including third-harmonic injection carrier-based PWM (THIPWM), offset addition carrier-based PWM (OAPWM), flat top carrier-based PWM (FTPWM) and space vector modulation (SVM). On comparison with Simple PWM, the switching techniques of THIPWM, OAPWM, FTPWM and SVM have many advantages such as lower total harmonic distortion (THD), minimal number of switching to decrease switching losses and the output fundamental voltage is increased. All of these systems are compared from view point of power quality and the limits of IEEE 519 standard are taken into account.