Single-phase AC/DC/AC converter using cascaded multilevel inverter

This paper presents the development of single phase AC/DC/AC converter using three-leg inverter. A uniform fixed switching frequency method of current control for both AC/DC and DC/AC converter stages has been proposed. A multiple control loop is used to control the input AC current and DC link voltages of the AC/DC converter and a cascaded H-bridge multilevel inverter (CHBMLI) is used to obtain the multilevel AC output voltage for the DC/AC inverter. The ramp comparison method of current control facilitates the fixed switching frequency operation of the converter to provide uniform switching cycle for all the switches of the AC/DC converter. A unipolar multi-carrier PWM has been used for the cascaded H-bridge multilevel inverter to yield the uniform and fixed switching frequency operation for the DC/AC inverter. This also gives AC output wherein the switching components are shifted at higher frequency hence yield better quality output. The results are verified through the PSCAD/EMTDC simulation studies.