Quasi Square Wave Modulation With Voltage Transformation Ability Applied to Modular Multilevel DC-DC Converter

With the increasing demand of electric energy, high voltage dc transmission (HVDC) system is supposed to be an efficient solution. Dc-dc converters play an indispensable role in the interconnection of dc systems with different voltage levels. This paper focuses on the modulation strategy of front-to-front dc-dc converter based on the modular multilevel converter (MMC). Dc-dc converters with this topology is suitable for highvoltage and high-power dc power transmission due to its modularity and reliability. On this basis, a quasi square wave phase-shift modulation strategy with voltage transformation ability is proposed to improve the performance of the modular multi-level de-de converter. The proposed modulation strategy can flexibly alter the voltage ratio while using a 1:1 ac transformer and the voltage stress of each submodule switch is controllable. Simulation results in MATLAB/Simulink validates the proposed modulation strategy.