New pre-charging scheme for MMC-based back-to-back HVDC system operated in nearest level control

Modular Multi-level Converter (MMC) has been widely researched in order to apply it for the back-to-back (BTB) high voltage direct current (HVDC) system. This paper proposes a new pre-charging scheme for the sub-module capacitors of MMC that is operated in nearest level control (NLC) modulation. The proposed scheme does not require any additional circuit or pulse width modulation (PWM) technique. The feasibility of proposed scheme was verified through computer simulations and experiments for a 3-phase 10kVA MMC with 12 sub-modules per each arm. The proposed scheme could be directly applied for the actual MMC-based HVDC system.