Full bridge MMC converter optimal design to HVDC operational requirements

Abstract

Abstract-Design and operation of FB (full bridge) MMC that meets HVDC specifications are studied in this paper. Three new design parameters: the over-modulation index (k MMC ), the DC modulation index (M dc ), the minimal DC voltage (V minpu ) are introduced to specify the operation of a FB MMC. Power increase and semiconductor count increase with the increase of k MMC is analyzed to understand benefits of over-modulation. The required number of submodules and the number of more-costly FB submodules for specified rated dc voltage, V minpu and k MMC are calculated. The relationship of the submodule inserting logic and dynamics of an arm is analyzed. The submodule voltage balancing is studied and the constraints on the required number of FB submodules are deduced. The capability of over-modulation and the operation under low DC voltage with optimal submodule count are verified using EMTP simulation.