Six-Level Hybrid Diode-Clamped Inverter Topology and DC-link Capacitor Voltage Balancing Control

This article proposes a six-level hybrid diode-clamped inverter (6L-HDCI) topology with the capability of self-balancing the dc-link capacitor voltages. It consists of two three-level neutral-point-clamped cells, one half-bridge cell in each phase, and five common dc-link capacitors. The proposed 6L-HDCI topology offers simple structure, cost savings, and lower power losses compared to the conventional 6L-DCI and 6L-FCI topologies, with a total cost reduction of 18.7% and 13.5%, respectively. Moreover, unlike the other topologies, which require auxiliary balancing circuits, for regulating the dc-link capacitor voltages, an algorithm is proposed for balancing these voltages over the full range of modulation indices without additional components. The top and bottom capacitor voltages at the dc-link can be balanced by injecting a zero-sequence voltage, whereas the inner three capacitor voltages are controlled by adjusting the duty ratio using PI controllers. The effectiveness of the proposed 6L-HDCI topology and voltage balancing control has been verified by simulation results. Finally, experimental results for the prototype hardware have validated the feasibility of the proposed topology and control.