Voltage Balancing Approaches for Diode-Clamped Multilevel Converters Using Auxiliary Capacitor-Based Circuits

An auxiliary capacitor-based balancing approach is adopted in this paper to equalize the dc-link capacitor voltages of a diode-clamped multilevel converter (DCMC). Four balancing circuits, including the generalized, one-level-capacitor, one-capacitor, and simplified one-capacitor-based configurations are discussed for a five-level DCMC system. These configurations are different in connection of the auxiliary circuits and numbers of the capacitors and switches, but they work on the same principle called ping-pong operation by utilizing the auxiliary capacitor as an equalizer between the capacitors of different voltages. The unbalance phenomenon, ping-pong principle, circuit configurations, and their switching schemes are analyzed, respectively. The superiorities of the proposed approach include balancing operation regardless of load power factor and modulation index, control simplicity, and independence from main circuits when compared to the traditional approaches. Simulations and experimental results verified the performances using the proposed balancing circuits and control strategies.