Two operational modes of the modular multilevel DC converter

Due to the increasing application of high voltage dc transmission, bidirectional dc to dc converters for high voltage applications will play a key role in future power grids. The recently presented modular multilevel dc converter (M2DC) is a new topology suitable for highvoltage bidirectional dc conversion. Two operational modes — inductive coupled mode and resistive coupled mode — of the M2DC are defined according to the characteristic of the arm impedance. Transfer functions of both operational modes are theoretically derived, which show that the M2DC could be configured to be either voltage source or current source. This feature offers the M2DC full controllability over output voltage and output current, making it suitable for different application scenarios. Simulation and experimental results of a 4 submodules tuned filter version M2DC are presented for verification of its functions.