Investigation and Design of a Modular Multilevel Converter in AFE Mode with Minimized Passive Elements
Proper sizing of the arm inductances is crucial for the MMC AFE. At higher powers and cur-rents, the main issue with the MMC AFE is the design of large arm inductances capable of re-stricting the input current in case of a fault on the MMC's DC bus. In high current MMC AFEs, where it becomes non-beneficial to design huge inductances, using an H-bridge-based MMC is proposed as a solution, as it has an intrinsic capability to suppress fault currents.
In this paper, an AFE MMC is designed with special focus on minimizing the passive elements' size, while keeping the same power quality and fault protection level. No additional con-roller is added in order to reduce the size of the passive elements. The proposed design can extend the operation range of the half-bridge-based MMC AFE by decreasing the amount of inductances needed. The performed reduction of passive elements (i.e., arm inductances and submodule capacitances) will result in reduced initial investment costs, and of active power loss in the passive elements.