Three-phase four-wire AC-DC-AC multilevel topologies obtained from an interconnection of three-leg converters

This paper investigates three AC-DC-AC multilevel topologies for three-phase four-wire (3P4W) applications obtained from an interconnection of three-leg voltage source converters (VSCs). The topologies provide bidirectional power flow and can be applied in line voltage regulators, universal active power filters and uninterrupted power supplies (UPS). Operating principles, a pulse-width modulation (PWM) technique and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the DC-link voltage and to optimize the harmonic distortion, reducing switching stress and power losses. Simulation results are used to compare the proposed configuration with a conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results are presented to validate the theoretical considerations and were obtained by using IGBTs with dedicated drives and a digital signal processor (DSP) with appropriated plug-in boards and sensors.