Control and Analysis of the Modular Multilevel DC De-Icer With STATCOM Functionality

De-icing of overhead transmission lines is necessary to prevent damage to the transmission system and outages. In this paper, a modular multilevel dc De-Icer (M2D2) is introduced, based on the structure of the modular multilevel converter with full-bridge submodules. The M2D2 exhibits a lot of salient features: high modularity, scalability, compactness, high efficiency, wide dc voltage range, and no harmonic filter requirements, etc. Moreover, during good weather, the M2D2 can be configured as a static synchronous compensator, providing reactive power support to the grid and alleviating power quality problems. Operating principle of the M2D2 is explained, harmonic features under phase-shifted carrier modulation are analyzed, and selections of the phase-shifted angle are derived to achieve best harmonic performance. Control schemes for the M2D2 are also developed, including control of de-icing current, capacitor voltages, and reactive power. Finally, experimental results, utilizing a downscaled prototype, confirm the validity of this topology and effectiveness of the proposed control strategies.