Multilevel Rectifier Based On Cascaded Transformer With Single DC-link and Shared Legs

This work presents multilevel rectifiers with single dc-link based on the concept of cascaded transformer with shared-leg converters, isolated from the ac-side, and a three-phase bridge converter connected directly with the ac-side. The shared-leg converters are generalized for n-stages. This feature are an option to increase the number of levels per number of legs and also saves the transformers count in comparison with the conventional cascaded transformer topologies. The transformers turns ratios are considered to maximize the number of levels equally spaced from each other. Hence, the quality of the waveform synthesized by resultant voltages are improved, which permits to reduce the total harmonic distortion (THD) content of converter voltages/currents and, as a consequence, the THD of grid currents. Reduction in the number of controlled switches is proposed and the proposed topologies are compared with conventional ones. Power factor correction is also presented by means of the control strategy. System model description, pulsewidth modulation (PWM) technique and control strategy are presented. Simulation and Experimental results are presented and discussed for validation purposes.