AC/DC/AC converter based on parallel AC/DC and cascaded multilevel DC/AC converter

This paper presents a single phase AC/DC/AC converter based on parallel AC/DC and cascaded multi-level DC/AC Converter. For a two-cell AC/DC/AC converter, two units of full-bridges are connected in parallel and two units of half-bridges are connected in cascade. It is proposed that instead of using two separate control loops of DC link voltages at the AC to DC conversion stage, only a single control loop with only one voltage sensor is proposed in this paper when two cells are equally loaded. It is also shown that by controlling only one cell DC link voltage, the other dc link voltage also gets controlled automatically. In addition, the power factor is also improved to unity at the AC side of the AC/DC conversion stage. Use of simple and unipolar ramp comparison control at both the stages leads to fixed switching frequency operation of all the switches along with the improved quality of input current and output voltage as compared to simple PWM control. The simulation result for the proposed topology has been obtained through the PSCAD/EMTDC simulation studies, for a two-cell based parallel cum cascaded AC/DC/AC converter. The experimental verification of the proposed topology and control strategy has been obtained using LABVIEW FPGA module with the help of PCI-7831R data acquisition board.