A Novel DC Voltage Control Method for STATCOM Based on Hybrid Multilevel H-Bridge Converter

This paper presents a transformerless static synchronous compensator (STATCOM) system based on hybrid multilevel H-bridge converter with delta configuration. This hybrid multilevel STATCOM is characterized by per-phase series connection of a high-voltage H-bridge converter operating at fundamental frequency and a low-voltage H-bridge converter operating at 5 kHz without any other circuit for dc voltage control. A new control strategy is proposed in this paper with focus on dc voltage regulation. Clustered balancing control is realized by injecting a zero-sequence current to the delta-loop, while individual voltage control is achieved by adjusting the fundamental content of ac quasi-square-waveform voltage of high-voltage converter. A downscaled experimental prototype rated at 100 V and 3 kVA is constructed in author's laboratory. Experimental results show that the hybrid multilevel STATCOM performs satisfactory not only improving efficiency and waveform quality, but also compensating reactive power and negative-sequence current while maintaining dc voltage at the given value.