PROJECT TITLE :

Simplified model and submodule capacitorvoltage balancing of single-phase AC/ACmodular multilevel converter for railwaytraction purpose - 2016

ABSTRACT:

One-phase AC/AC modular multilevel converter (MMC) will interact directly with 25 kV railway grid without a bulky 50 Hz step-down transformer. This brings in great savings in size and value. Submodule (SM) voltage balancing of this sort of MMCs remains a significant technique issue. This study proposes a voltage-balancing resolution for this situation that consists of intra- and inter-arm voltage balancing methods. The former combines the benefits of carrier phase-shifted pulse-width modulation (PWM) and phase disposition PWM based voltage-balancing ways. It solely uses 2 proportional regulators, easing the management system considerably. The latter relies on an influence channel between the upper and lower arms. It avoids interferences with input/output voltage and current, and takes out common mode current element which would be injected into the grid with typical inter-arm balancing strategies. By assuming excellent voltage-balancing, a simplified mathematical model is also developed, which reveals a lot of clearly the ability conversion relationship. Simulations and experiments verify the proposed voltage-balancing strategies and the mathematical model.