Evaluation of different PWM techniques for two level inverter in grid connected WECS

Abstract

In this paper we present evaluation of two pulse width modulation techniques for two level inverters employed in a grid connected wind energy conversion systems(WECS). Sine pulse width modulation is the most simple modulation technique employed for inverters. However it has disadvantages like very narrow linear range, higher total harmonic distortion value(THD) and does not make effective utilization of DC value. The other modulation technique is space vector modulation (SVPWM), which eliminates lower order harmonics and provides a lower THD, high reliability and optimized efficiency when compared sine pulse width modulation(SPWM). The induction machine here is driven by a variable speed wind turbine and AC voltage generated is rectified by the voltage source converter and stored in a DC link capacitor. Control strategy has been developed for maintaining this DC link voltage constant at a reference value. This DC voltage is further inverted and fed to grid with a current controlled voltage source inverter (CCVSI). A current control strategy for CCVSI has also been developed. The results of the developed system validates the theoretical studies.