Topology and Control of Seven-Level Tree-Type Active Neutral-Point-Clamped Converters

To reduce the overall device count of neutral-point-clamped (NPC) multilevel converters for a further increased power density, two tree-type seven-level active NPC (7L-TANPC) converters are proposed in this article. Compared with the existing seven-level NPC-based topologies, the proposed 7L-TANPC converters have a smaller device count with lower total device standing voltage, which can improve the power density with reduced cost. To ensure their operation with balanced dc-link capacitor voltages, a carrier-overlapped pulse width modulation, as well as its related active capacitor voltage balancing methods by zero-sequence voltage injection and duty cycle adjustments, are also proposed in this article. Simulation and experimental results verify the validity of the proposed topologies, modulation and control methods.