Novel Control Scheme of Three-Phase Six-Level Hybrid Flying-Capacitor Inverters With Self-Balancing Capability

In this paper, a novel control scheme is proposed for the recently developed six-level hybrid flying-capacitor inverter. In the conventional scheme, an auxiliary balancing circuit is required to regulate the voltages of split DC-link capacitors. This results in the increased device count and converter volume, and thus diminishes the competitiveness of this topology. In order to eliminate these auxiliary components, a novel control scheme is proposed based on zero-sequence voltage (ZSV) injection to the phase-shifted modulation voltages. This method has enabled a simultaneous control of all split DC-link and flying capacitor voltages through the regulation of closely-linked key parameters affecting these voltages, resulting in the self-balancing capability with low voltage ripples (lower than 10 % of the references). The proposed technique has been verified with simulation and experimental results.