A Multilevel DC-Link Converter for VSC-HVDC Application

This paper proposes a novel topology of AC-DC converter with multilevel DC-link. Sub-valves are connected in series to generate a DC voltage with interleaved superimposition. Each sub-valve includes both a switched-capacitor chain to generate modulation waveform and a H-bridge to half-flip the wave. Modular-designed units help to realize the voltage sharing as well as the floating supply of IGBTs. Its mathematical model is analyzed in detail. Then the voltage regulation method and optimal operating point is given. Finally, the feasibility is verified by simulation. Compared with MMC, the arm capacitance and IGBT devices in MDC are reduced 86% and 14.8% respectively. It has significant technical economy and prospect in VSC-HVDC application.