Multilevel Inverter Topology Using Multiple Level Doubling Networks and Single DC Source Per Phase

A high-resolution asymmetrical multilevel converter (MLI) with single dc source per phase is introduced in this paper. Objective of the proposed MLI is to remove all the isolated auxiliary dc sources of the MLI by floating-capacitors. The topology consists of multiple cell (bridge) groups. Each of the cell group consist a full-bridge with certain dc-bus voltage and a half-bridge with dc-bus voltage half of that corresponding full bridge. All the DC bus capacitors of the half-bridges are balanced without closed-loop control using the principle of level doubling network, while the capacitors of the auxiliary full-bridges are balanced in closed-loop. In order to ensure voltage balancing of all the floating capacitors, it is required to limit the maximum voltage-ratio between the cell groups to be
${{1:5:}}\,\,{{ \ldots :}}{{{5}}^{{n}}}$
(for n number of cell groups). A simulation model is formed with a single dc source and 12 switches per phase (two cell groups per phase). Total 43 levels are achieved in line to line voltage with only two cell-groups (only 12 switches per phase) and one dc source per phase. Simulation results using MATLAB/Simulink platform matched well with the theory.