EXPERIMENTAL INVESTIGATIONS OF A MULTILEVEL CONVERTER SUITABLE FOR MEDIUM VOLTAGE DRIVES

Abstract

In this dissertation multi-level PWM buck-boost converter is discussed. The proposed scheme uses a multi-winding phase shifting transformer. The transformer is designed for a three phase input primary which may be connected in star or delta and four three phase secondaries. The four secondary winding voltages are phase shifted from each other by an angle of 150 and these are phase shifted with respect to primary by an angle of +22.5°, +7.5°,-7.5°and -22.5° respectively. These outputs feed four three phase rectifier units to which buck-boost arrangement is connected. The scheme uses pulse width modulation technique to generate firing -pul-ses -to- these- sw-itches. The main objective of this scheme is to control the voltage level, reduce harmonics, make input line current sinusoidal and improve power factor. IGBT's are used as semiconductor switches in chopper which is operated in both continuous and discontinuous mode. Whole system is operated in open loop as well as in closed loop mode and their performance is studied. The experimental results are also verified with simulated results.