Ripple Ports Arrangements in DAB Assisted Modular Multilevel Converter for Low Voltage Applications

Modular Multilevel Converters efficiency, modularity and power quality make them perfectly suitable for high and medium voltage applications. The main drawbacks are the high capacitances required, numerous measurements system and high control complexity. These problems make the converter unsuitable for low voltage applications, mainly because of the limited space and the complexity involved. In order to solve these issues modification to the classical MMC topology has been proposed. This work presents the design and arrangements of ripple ports to equalize the floating capacitor voltages when a low value of capacitance is considered, considering Dual Active Bridge converters as the main block to interlink the MMC Sub-Modules. The proposed work considers open loop control of the DAB converters analyzing the two main arrangements, series and parallel, of the ripple ports, deriving fundamental equations and considering operation at zero phase shift for the DAB. The obtained MMC structures are validated through simulations.