Modular multilevel converter based on full bridge cells for Multi-Terminal DC transmission

In the Multi-Terminal DC (MTDC) power transmission system, the power flows according to the DC voltages of the terminals and the line impedances. And, the power flowing through each DC line in the mesh MTDC system is not able to be controlled independently. In this paper, a Modular Multilevel Converter based on Full Bridge cells (MMC-FB) is proposed for auxiliary voltage control in the mesh type MTDC system. To control the MMC-FB in four-quadrant, the capacitor voltage balancing method is also proposed with three equivalent circuit models. All control algorithm associated with the proposed MTDC has been confirmed by computer simulation.