Topology and Control of a Five-Level Hybrid-Clamped Converter for Medium-Voltage High-Power Conversions

Five-level hybrid-clamped (5L-HC) converter is a newly proposed topology which is suitable for high-performance medium-voltage high-power conversions without switches directly connected in series. The critical issue of this converter is that two flying capacitor voltages of each phase and two neutral-point potentials of the dc-link need to be balanced. This paper presents a decoupled voltage balancing method for this 5L-HC converter based on modified phase-shifted pulse width modulation (PS-PWM) and optimal zero-sequence voltage injection. The voltages across the central dc-link capacitor and two flying capacitors are balanced first by adjusting the width of four PWM signals. Second, the relationship between the neutral-point currents and the output phase voltage is studied and the upper and lower dc-link capacitor voltages are balanced by zero-sequence voltage injection. Both steady-state and dynamic-state simulation and experimental results are presented to confirm the validity of this method.