APPLYING PWM TO CONTROL OVERCURRENTS AT UNBALANCED FAULTS OF FORCED-COMMUTATED VSCS USED AS STATIC VAR COMPENSATORS

This study is devoted to investigating the possibility of controlling the overcurrent of a forced-commutated voltage source converter (VSC) by PWM when the ac system is undergoing large unbalanced disturbance. The converter is supposed to be used as a static var compensator at a high power level. A novel control strategy is proposed for controlling the reactive current and the dc side voltage independently. Digital s imulation results are presented and compared with the results by using just the reactive current control with fundamental switching frequenc y.